diff --git a/config/packages/validator.yaml b/config/packages/validator.yaml
index 3fcd3f82e1..a695e1a62a 100644
--- a/config/packages/validator.yaml
+++ b/config/packages/validator.yaml
@@ -1,4 +1,3 @@
 framework:
     validation:
         email_validation_mode: html5
-
diff --git a/public/main/exercise/exercise.class.php b/public/main/exercise/exercise.class.php
index 259d086cf4..681b1d09e1 100644
--- a/public/main/exercise/exercise.class.php
+++ b/public/main/exercise/exercise.class.php
@@ -183,7 +183,7 @@ class Exercise
 
         // if the exercise has been found
         if ($object = Database::fetch_object($result)) {
-            $this->id = $this->iId = $object->iid;
+            $this->id = $this->iId = (int) $object->iid;
             $this->exercise = $object->title;
             $this->name = $object->title;
             $this->title = $object->title;
diff --git a/public/main/exercise/question_pool.php b/public/main/exercise/question_pool.php
index 7b29135884..4067b036c0 100644
--- a/public/main/exercise/question_pool.php
+++ b/public/main/exercise/question_pool.php
@@ -2,6 +2,7 @@
 /* For licensing terms, see /license.txt */
 
 use Chamilo\CoreBundle\Entity\ExtraField as ExtraFieldEntity;
+use Chamilo\CoreBundle\Framework\Container;
 use ChamiloSession as Session;
 use Knp\Component\Pager\Paginator;
 
@@ -294,27 +295,6 @@ if (isset($_REQUEST['action'])) {
     }
 }
 
-Display::display_header($nameTools, 'Exercise');
-
-// Menu
-echo '<div class="actions">';
-if (isset($fromExercise) && $fromExercise > 0) {
-    echo '<a href="admin.php?'.api_get_cidreq().'&exerciseId='.$fromExercise.'">'.
-            Display::return_icon('back.png', get_lang('Go back to the questions list'), '', ICON_SIZE_MEDIUM).'</a>';
-    $titleAdd = get_lang('Add question to test');
-} else {
-    echo '<a href="exercise.php?'.api_get_cidreq().'">'.
-        Display::return_icon('back.png', get_lang('BackToTestsList'), '', ICON_SIZE_MEDIUM).'</a>';
-    echo "<a href='admin.php?exerciseId=0'>".
-        Display::return_icon('add_question.gif', get_lang('New question'), '', ICON_SIZE_MEDIUM).'</a>';
-    $titleAdd = get_lang('Manage all questions');
-}
-echo '</div>';
-
-if ('' != $displayMessage) {
-    echo Display::return_message($displayMessage, 'confirm');
-}
-
 // Form
 $sessionList = SessionManager::get_sessions_by_user(api_get_user_id(), api_is_platform_admin());
 $session_select_list = ['-1' => get_lang('Select')];
@@ -449,7 +429,6 @@ if (!empty($_course)) {
 
 // Answer type list
 $form = new FormValidator('question_pool', 'GET', $url);
-$form->addHeader($nameTools.' - '.$titleAdd);
 $form->addHidden('fromExercise', $fromExercise);
 $form
     ->addSelect(
@@ -514,14 +493,13 @@ $jsForExtraFields = $extraField->addElements($form, 0, [], true);
 
 $form->addButtonFilter(get_lang('Filter'), 'name');
 
-echo $form->display();
+if (isset($fromExercise) && $fromExercise > 0) {
+    $titleAdd = get_lang('Add question to test');
+} else {
+    $titleAdd = get_lang('Manage all questions');
+}
 
-echo '<script>$(function () {
-        '.$jsForExtraFields['jquery_ready_content'].'
-    })</script>';
-?>
-<div class="clear"></div>
-<?php
+$form->addHeader($nameTools.' - '.$titleAdd);
 
 /**
  * @return array
@@ -880,12 +858,28 @@ if (empty($length)) {
 
 $start = ($page - 1) * $length;
 
-$paginator = new Paginator();
-$pagination = $paginator->paginate([]);
+$mainQuestionList = getQuestions(
+    false,
+    $start,
+    $length,
+    $exerciseId,
+    $courseCategoryId,
+    $selected_course,
+    $session_id,
+    $exerciseLevel,
+    $answerType,
+    $questionId,
+    $description,
+    $fromExercise,
+    $formValues
+);
+
+$paginator = new Paginator(Container::$container->get('event_dispatcher'));
+$pagination = $paginator->paginate($mainQuestionList, $page, $length);
+
 $pagination->setTotalItemCount($nbrQuestions);
 $pagination->setItemNumberPerPage($length);
 $pagination->setCurrentPageNumber($page);
-
 $pagination->renderer = function ($data) use ($url) {
     $render = '';
     if ($data['pageCount'] > 1) {
@@ -903,22 +897,6 @@ $pagination->renderer = function ($data) use ($url) {
     return $render;
 };
 
-$mainQuestionList = getQuestions(
-    false,
-    $start,
-    $length,
-    $exerciseId,
-    $courseCategoryId,
-    $selected_course,
-    $session_id,
-    $exerciseLevel,
-    $answerType,
-    $questionId,
-    $description,
-    $fromExercise,
-    $formValues
-);
-
 // build the line of the array to display questions
 // Actions are different if you launch the question_pool page
 // They are different too if you have displayed questions from your course
@@ -1045,8 +1023,35 @@ $headers = [
     $actionLabel,
 ];
 
-echo $pagination;
+Display::display_header($nameTools, 'Exercise');
+
+// Menu
+echo '<div class="actions">';
+if (isset($fromExercise) && $fromExercise > 0) {
+    echo '<a href="admin.php?'.api_get_cidreq().'&exerciseId='.$fromExercise.'">'.
+        Display::return_icon('back.png', get_lang('Go back to the questions list'), '', ICON_SIZE_MEDIUM).'</a>';
+} else {
+    echo '<a href="exercise.php?'.api_get_cidreq().'">'.
+        Display::return_icon('back.png', get_lang('BackToTestsList'), '', ICON_SIZE_MEDIUM).'</a>';
+    echo "<a href='admin.php?exerciseId=0'>".
+        Display::return_icon('add_question.gif', get_lang('New question'), '', ICON_SIZE_MEDIUM).'</a>';
+}
+echo '</div>';
+
+if ('' != $displayMessage) {
+    echo Display::return_message($displayMessage, 'confirm');
+}
+
+echo $form->display();
+
+echo '<script>$(function () {
+        '.$jsForExtraFields['jquery_ready_content'].'
+    })</script>';
+?>
+    <div class="clear"></div>
+<?php
 
+echo $pagination;
 $tableId = 'question_pool_id';
 echo '<form id="'.$tableId.'" method="get" action="'.$url.'">';
 echo '<input type="hidden" name="fromExercise" value="'.$fromExercise.'">';
@@ -1077,9 +1082,7 @@ foreach ($data as $rows) {
     }
     $row++;
 }
-
 $table->display();
-
 echo '</form>';
 
 $html = '<div class="btn-toolbar">';
@@ -1108,7 +1111,7 @@ if ($selected_course == api_get_course_int_id()) {
     $actions = ['reuse' => get_lang('Re-use in current testQuestion')];
 }
 
-foreach ($actions as $action => &$label) {
+foreach ($actions as $action => $label) {
     $html .= '<li>
             <a
                 data-action ="'.$action.'"
diff --git a/public/main/inc/ajax/exercise.ajax.php b/public/main/inc/ajax/exercise.ajax.php
index 6b6001c9d8..b1b20cd284 100644
--- a/public/main/inc/ajax/exercise.ajax.php
+++ b/public/main/inc/ajax/exercise.ajax.php
@@ -2,13 +2,13 @@
 
 /* For licensing terms, see /license.txt */
 
-use Chamilo\CoreBundle\Entity\TrackEExerciseConfirmation;
 use Chamilo\CoreBundle\Entity\TrackEExercises;
+use Chamilo\CoreBundle\Entity\TrackEExerciseConfirmation;
 use ChamiloSession as Session;
 
 require_once __DIR__.'/../global.inc.php';
 $current_course_tool = TOOL_QUIZ;
-$debug = false;
+$debug = true;
 api_protect_course_script(true);
 $action = $_REQUEST['a'];
 $course_id = api_get_course_int_id();
@@ -39,7 +39,6 @@ switch ($action) {
         echo json_encode($data);
         break;
     case 'update_duration':
-
         if (Session::read('login_as')) {
             if ($debug) {
                 error_log("User is 'login as' don't update duration time.");
@@ -68,8 +67,8 @@ switch ($action) {
         $onlyUpdateValue = 10;
 
         $em = Database::getManager();
-        /** @var \Chamilo\CoreBundle\Entity\TrackEExercises $attempt */
-        $attempt = $em->getRepository('ChamiloCoreBundle:TrackEExercises')->find($exeId);
+        /** @var TrackEExercises $attempt */
+        $attempt = $em->getRepository(TrackEExercises::class)->find($exeId);
 
         if (empty($attempt)) {
             if ($debug) {
@@ -90,14 +89,14 @@ switch ($action) {
             exit;
         }
 
-        if ($exerciseInSession->id != $exerciseId) {
+        if ($exerciseInSession->iId !== $exerciseId) {
             if ($debug) {
-                error_log("Cannot update, exercise are different.");
+                error_log('Cannot update, exercise are different.');
             }
             exit;
         }
 
-        if ('incomplete' != $attempt->getStatus()) {
+        if ('incomplete' !== $attempt->getStatus()) {
             if ($debug) {
                 error_log('Cannot update exercise is already completed.');
             }
@@ -125,20 +124,22 @@ switch ($action) {
                 $duration = (int) $duration;
                 if (!empty($duration)) {
                     if ($debug) {
-                        error_log("Exe_id: #".$exeId);
+                        error_log('Exe_id: #'.$exeId);
                         error_log("Key: $key");
                         error_log("Exercise to update: #$exerciseId of user: #$userId");
                         error_log("Duration time found in DB before update: $durationFromObject");
                         error_log("Current spent time $sessionTime before an update");
                         error_log("Accumulate duration to save in DB: $duration");
-                        error_log("End date (UTC) before update: ".$attempt->getExeDate()->format('Y-m-d H:i:s'));
-                        error_log("End date (UTC) to be save in DB: ".$nowObject->format('Y-m-d H:i:s'));
+                        error_log('End date (UTC) before update: '.$attempt->getExeDate()->format('Y-m-d H:i:s'));
+                        error_log('End date (UTC) to be save in DB: '.$nowObject->format('Y-m-d H:i:s'));
                     }
                     $attempt
                         ->setExeDuration($duration)
                         ->setExeDate($nowObject);
                     $em->persist($attempt);
                     $em->flush();
+
+                    echo 1;
                 }
             } else {
                 if ($debug) {
@@ -288,7 +289,7 @@ switch ($action) {
                     $timeInfo = api_convert_and_format_date(
                             $row['start_date'],
                             DATE_TIME_FORMAT_LONG
-                        ).' ['.($h > 0 ? $h.':' : '').sprintf("%02d", $m).':'.sprintf("%02d", $s).']';
+                        ).' ['.($h > 0 ? $h.':' : '').sprintf('%02d', $m).':'.sprintf('%02d', $s).']';
                 } else {
                     $timeInfo = api_convert_and_format_date(
                         $row['start_date'],
@@ -303,7 +304,7 @@ switch ($action) {
                     round($row['score'] * 100).'%',
                 ];
                 $response->rows[$i]['cell'] = $array;
-                $i++;
+                ++$i;
             }
         }
         echo json_encode($response);
@@ -327,7 +328,7 @@ switch ($action) {
                         'c_id' => $course_id,
                     ]
                 );
-                $counter++;
+                ++$counter;
             }
             echo Display::return_message(get_lang('Saved..'), 'confirmation');
         }
@@ -357,7 +358,7 @@ switch ($action) {
                     ]
                 )
                 ;
-                $counter++;
+                ++$counter;
             }
             echo Display::return_message(get_lang('Saved..'), 'confirmation');
         }
@@ -420,10 +421,10 @@ switch ($action) {
             if ($debug) {
                 error_log("exe_id = $exeId");
                 error_log("type = $type");
-                error_log("choice = ".print_r($choice, 1)." ");
-                error_log("hot_spot_coordinates = ".print_r($hot_spot_coordinates, 1));
-                error_log("remind_list = ".print_r($remind_list, 1));
-                error_log("--------------------------------");
+                error_log('choice = '.print_r($choice, 1).' ');
+                error_log('hot_spot_coordinates = '.print_r($hot_spot_coordinates, 1));
+                error_log('remind_list = '.print_r($remind_list, 1));
+                error_log('--------------------------------');
             }
 
             // Exercise information.
@@ -439,10 +440,10 @@ switch ($action) {
                 echo 'error';
                 if ($debug) {
                     if (empty($question_list)) {
-                        error_log("question_list is empty");
+                        error_log('question_list is empty');
                     }
                     if (empty($objExercise)) {
-                        error_log("objExercise is empty");
+                        error_log('objExercise is empty');
                     }
                 }
                 exit;
@@ -555,7 +556,6 @@ switch ($action) {
 
                 $my_choice = isset($choice[$my_question_id]) ? $choice[$my_question_id] : null;
 
-
                 // Creates a temporary Question object
                 $objQuestionTmp = Question::read($my_question_id, $objExercise->course);
 
@@ -774,7 +774,7 @@ switch ($action) {
                 // Destruction of the Question object
                 unset($objQuestionTmp);
                 if ($debug) {
-                    error_log("---------- end question ------------");
+                    error_log('---------- end question ------------');
                 }
             }
             if ($debug) {
@@ -800,15 +800,15 @@ switch ($action) {
 
         if (ONE_PER_PAGE == $objExercise->type) {
             if ($debug) {
-                error_log("result: one_per_page");
-                error_log(" ------ end ajax call ------- ");
+                error_log('result: one_per_page');
+                error_log(' ------ end ajax call ------- ');
             }
             echo 'one_per_page';
             exit;
         }
         if ($debug) {
-            error_log("result: ok");
-            error_log(" ------ end ajax call ------- ");
+            error_log('result: ok');
+            error_log(' ------ end ajax call ------- ');
         }
         echo 'ok';
         break;
diff --git a/public/main/inc/lib/usergroup.lib.php b/public/main/inc/lib/usergroup.lib.php
index 64755d57e1..8ff069ee9d 100644
--- a/public/main/inc/lib/usergroup.lib.php
+++ b/public/main/inc/lib/usergroup.lib.php
@@ -2856,7 +2856,6 @@ class UserGroup extends Model
             $direction = 'ASC';
         }
 
-        $from = (int) $from;
         $sql .= " LIMIT $from, $number_of_items";
 
         $res = Database::query($sql);
diff --git a/src/CoreBundle/EventSubscriber/PaginationSubscriber.php b/src/CoreBundle/EventSubscriber/PaginationSubscriber.php
new file mode 100644
index 0000000000..141396378c
--- /dev/null
+++ b/src/CoreBundle/EventSubscriber/PaginationSubscriber.php
@@ -0,0 +1,43 @@
+<?php
+
+/* For licensing terms, see /license.txt */
+
+namespace Chamilo\CoreBundle\EventSubscriber;
+
+use Knp\Component\Pager\Event\ItemsEvent;
+use Knp\Component\Pager\Event\PaginationEvent;
+use Knp\Component\Pager\Pagination\SlidingPagination;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+
+class PaginationSubscriber implements EventSubscriberInterface
+{
+    protected $defaultLocale;
+    protected $parameterBag;
+    protected $settingsManager;
+
+    public function items(ItemsEvent $event)
+    {
+        if (is_array($event->target)) {
+            $event->items = $event->target;
+            $event->count = count($event->target);
+            $event->stopPropagation();
+        }
+    }
+
+    public function pagination(PaginationEvent $event)
+    {
+        if (is_array($event->target)) {
+            $event->setPagination(new SlidingPagination);
+        }
+
+        $event->stopPropagation();
+    }
+
+    public static function getSubscribedEvents()
+    {
+        return [
+            'knp_pager.items' => ['items', 1/*increased priority to override any internal*/],
+            'knp_pager.pagination' => ['pagination', 0]
+        ];
+    }
+}