--- editrandom_orig.php	2020-03-09 19:29:59.000000000 +0100
+++ editrandom.php	2020-05-15 03:56:03.229863800 +0200
@@ -133,10 +133,8 @@
     }, $currentslottags);
 
     foreach ($tags as $tag) {
-        if ($key = array_search(['tagid' => $tag->id, 'tagname' => $tag->name], $searchableslottags)) {
-            // If found, $key would be the id field in the quiz_slot_tags table.
-            // Therefore, there was no need to check !== false here.
-            $recordstokeep[] = $key;
+        if (in_array(['tagid' => $tag->id, 'tagname' => $tag->name], $searchableslottags)) {
+            $recordstokeep[] = $tag->id;
         } else {
             $recordstoinsert[] = (object)[
                 'slotid' => $slot->id,
@@ -149,7 +147,7 @@
     // Now, delete the remaining records.
     if (!empty($recordstokeep)) {
         list($select, $params) = $DB->get_in_or_equal($recordstokeep, SQL_PARAMS_QM, 'param', false);
-        $DB->delete_records_select('quiz_slot_tags', "id $select", $params);
+        $DB->delete_records_select('quiz_slot_tags', "slotid = {$slot->id} AND tagid {$select}", $params);
     } else {
         $DB->delete_records('quiz_slot_tags', array('slotid' => $slot->id));
     }