diff --git a/classes/local/table/remaining_courses_table.php b/classes/local/table/remaining_courses_table.php
index 95b7121..bf2b28f 100644
--- a/classes/local/table/remaining_courses_table.php
+++ b/classes/local/table/remaining_courses_table.php
@@ -42,14 +42,17 @@ class remaining_courses_table extends \table_sql {
 
     private evasys_category $evasyscategory;
 
+    private bool $showbuttons;
+
     /**
      * Constructor for course_manager_table.
      */
-    public function __construct($categoryids, $semester, evasys_category $evasyscategory, $coursefullname = null) {
+    public function __construct($categoryids, $semester, evasys_category $evasyscategory, $coursefullname = null, bool $showbuttons = true) {
         parent::__construct('block_evasys_sync-course_manager_table');
         global $DB, $PAGE, $OUTPUT;
 
         $this->evasyscategory = $evasyscategory;
+        $this->showbuttons = $showbuttons;
 
         $fields = 'c.id as courseid, c.fullname as coursename, cfd.intvalue as semester';
 
@@ -134,7 +137,7 @@ public function col_teacher($row) {
      */
     public function col_tools($row) {
         global $PAGE, $OUTPUT;
-        if (!$this->evasyscategory->default_period_set()) {
+        if (!$this->evasyscategory->default_period_set() || !$this->showbuttons) {
             return '';
         }
         return $OUTPUT->render(new \single_button(new moodle_url($PAGE->url, ['action' => 'seteval', 'ids[]' => $row->courseid]),
@@ -155,7 +158,7 @@ public function wrap_html_finish() {
         parent::wrap_html_finish();
         echo "<br>";
 
-        if (!$this->evasyscategory->default_period_set()) {
+        if (!$this->evasyscategory->default_period_set() || !$this->showbuttons) {
             return;
         }
 
diff --git a/lang/de/block_evasys_sync.php b/lang/de/block_evasys_sync.php
index a531aa9..bccf373 100755
--- a/lang/de/block_evasys_sync.php
+++ b/lang/de/block_evasys_sync.php
@@ -290,3 +290,5 @@
 $string['missing_course_id'] = 'Fehlende Kurs-ID! Bitte wenden Sie sich an den Learnweb Support mit einem Link zu der Veranstaltung im HIS LSF, die evaluiert werden soll.';
 $string['no_evasys_course_found'] = 'Kein passender EvaSys-Kurs gefunden! Bitte wenden Sie sich an Ihren Evaluationskoordinator.';
 $string['not_inside_evaluation_category'] = 'Dieser Kurs ist in keiner Evaluationskategorie! Bitte wenden Sie sich an den Learnweb Support.';
+
+$string['previous_process_still_active'] = 'Diese Kurskategorie wird derzeit bereits bearbeitet. Bitte versuchen Sie es in Kürze erneut!';
diff --git a/lang/en/block_evasys_sync.php b/lang/en/block_evasys_sync.php
index 072d445..12dafce 100755
--- a/lang/en/block_evasys_sync.php
+++ b/lang/en/block_evasys_sync.php
@@ -301,3 +301,5 @@
 $string['missing_course_id'] = 'Missing course id! Please contact the Learnweb support with a link to the course in HIS LSF which should be evaluated.';
 $string['no_evasys_course_found'] = 'No matching EvaSys-Course found! Please contact your evaluation coordinator.';
 $string['not_inside_evaluation_category'] = 'This course isn\'t inside any evaluation category! Please contact the Learnweb support.';
+
+$string['previous_process_still_active'] = 'This course category is already being processed. Please try again shortly!';
diff --git a/managecategory_remaining.php b/managecategory_remaining.php
index 71fcca2..8a9e7c8 100644
--- a/managecategory_remaining.php
+++ b/managecategory_remaining.php
@@ -46,9 +46,18 @@
 
 $data = $cache->get($cachekey);
 
+$lockname = 'block_evasys_sync_process_category';
+$resource = 'evasyscat:' . $evasyscategory->get('id');
+$lockfactory = \core\lock\lock_config::get_lock_factory($lockname);
+$lock = $lockfactory->get_lock($resource, 0);
+
 $action = optional_param('action', null, PARAM_ALPHAEXT);
 if ($action === 'seteval') {
+    if (!$lock) {
+        throw new coding_exception(get_string('previous_process_still_active', 'block_evasys_sync'));
+    }
     require_sesskey();
+    core_php_time_limit::raise();
     $courses = required_param_array('ids', PARAM_INT);
     $errors = \block_evasys_sync\evaluation_manager::set_default_evaluation_for($courses, $evasyscategory);
     if ($errors) {
@@ -58,9 +67,16 @@
         }
         \core\notification::error($erroroutput);
     }
+    $lock->release();
     redirect($PAGE->url);
 }
 
+if ($lock) {
+    $lock->release();
+} else{
+    \core\notification::warning(get_string('previous_process_still_active', 'block_evasys_sync'));
+}
+
 $field = $DB->get_record('customfield_field', array('shortname' => 'semester', 'type' => 'semester'), '*', MUST_EXIST);
 $fieldcontroller = \core_customfield\field_controller::create($field->id);
 $datacontroller = \core_customfield\data_controller::create(0, null, $fieldcontroller);
@@ -72,7 +88,8 @@
 
 $catids = array_merge($category->get_all_children_ids(), [$category->id]);
 
-$table = new remaining_courses_table($catids, $data->semester ?? null, $evasyscategory, $data->coursename ?? null);
+$table = new remaining_courses_table($catids, $data->semester ?? null, $evasyscategory,
+        $data->coursename ?? null, (bool) $lock);
 $table->define_baseurl($PAGE->url);
 
 $PAGE->navigation->add('EvaSys', new moodle_url('/blocks/evasys_sync/manageroverview.php'))