diff --git a/application/Calendar/CalendarModel.php b/application/Calendar/CalendarModel.php
index ab035b5e4..60f494bfe 100644
--- a/application/Calendar/CalendarModel.php
+++ b/application/Calendar/CalendarModel.php
@@ -646,8 +646,6 @@ WHERE `TimerecordingCategory`.`hourday`!='1' AND `TimerecordingCategory`.`hourda
 
     public static function updateCalendarEvent($r, $me)
     {
-
-
         $description = ($r->description);
         $attachments = ($r->attachments);
         $location = ($r->location);
@@ -788,6 +786,8 @@ WHERE `TimerecordingCategory`.`hourday`!='1' AND `TimerecordingCategory`.`hourda
 
 
         $db->update("cal_events", $updateArray, "id = '" . $id . "'");
+//        error_log("=== NACH ERSTEM UPDATE ===");
+//        error_log("Suche nach linked events für Event ID: " . $id);
         if ($newkey) {
             $res = $db->select("cal_events_attachments", "id,cal_events_id", "1=1 AND cal_events_id  = '" . $cal_events_id . "'");
             if ($db->num_rows($res)) {
@@ -852,10 +852,33 @@ WHERE `TimerecordingCategory`.`hourday`!='1' AND `TimerecordingCategory`.`hourda
             $db->insert("TheTool_CalendarQueue", $data);
         }
         $resMain = $db->select("cal_events", 'linked_event_uid,is_organizer', "id = '" . $id . "' LIMIT 1");
+//        error_log("=== MAIN EVENT CHECK ===");
+//        error_log("num_rows: " . $db->num_rows($resMain));
         if ($db->num_rows($resMain)) {
+//            error_log("DEBUG: Vor fetch_object");
             $mainEvent = $db->fetch_object($resMain);
+//            error_log("DEBUG: Nach fetch_object");
+            if ($mainEvent && $mainEvent->is_organizer == 1 && empty($mainEvent->linked_event_uid)) {
+                $new_linked_uid = 'LINKED-' . strtoupper(uniqid()) . '-' . time();
+                $db->update("cal_events", array('linked_event_uid' => $new_linked_uid), "id = '" . $id . "'");
+                $mainEvent->linked_event_uid = $new_linked_uid;
+//                error_log("DEBUG: Alte Event - linked_event_uid erstellt: " . $new_linked_uid);
+            }
+            if (!$mainEvent) {
+//                error_log("ERROR: fetch_object returned false/null!");
+            } else {
+//                error_log("DEBUG: mainEvent Object: " . print_r($mainEvent, true));
+//                error_log("mainEvent->is_organizer: " . ($mainEvent->is_organizer ?? 'NULL'));
+//                error_log("mainEvent->linked_event_uid: " . ($mainEvent->linked_event_uid ?? 'NULL'));
 
-            if ($mainEvent->is_organizer == 1 && !empty($mainEvent->linked_event_uid)) {
+                if (isset($mainEvent->is_organizer) && isset($mainEvent->linked_event_uid)) {
+//                    error_log("Bedingung erfüllt? " . (($mainEvent->is_organizer == 1 && !empty($mainEvent->linked_event_uid)) ? "JA" : "NEIN"));
+                } else {
+//                    error_log("ERROR: is_organizer oder linked_event_uid nicht gesetzt!");
+                }
+            }
+
+            if ($mainEvent->is_organizer == 1 && ($mainEvent->linked_event_uid)) {
                 $sqlLinked = "SELECT ce.id, ce.calendar_id, cc.ms_user_id microsoft_id
                               FROM cal_events ce 
                               LEFT JOIN cal_calendars cc ON ce.calendar_id = cc.id 
@@ -995,10 +1018,19 @@ WHERE `TimerecordingCategory`.`hourday`!='1' AND `TimerecordingCategory`.`hourda
                                 $newAttendeeCalId = intval($emailCalData->go_calendar_id);
                             }
                         }
+                        error_log("=== NEUER TEILNEHMER CHECK ===");
+                        error_log("newAttendee Wert: " . print_r($newAttendee, true));
+                        error_log("newAttendeeCalId: " . ($newAttendeeCalId ?: 'NULL'));
+                        error_log("currentAttendeeCalendarIds: " . print_r($currentAttendeeCalendarIds, true));
+                        error_log("Ist in currentAttendeeCalendarIds? " . (in_array($newAttendeeCalId, $currentAttendeeCalendarIds) ? "JA" : "NEIN"));
+                        // DEBUG ENDE
+
+
                         if ($newAttendeeCalId) {
                             if (!in_array($newAttendeeCalId, $currentAttendeeCalendarIds)) {
                                 $newAttCal = self::search(array("go_calendar_id" => $newAttendeeCalId));
                                 if (count($newAttCal) > 0) {
+                                    // ÄNDERUNG: Prüfe ms_user_id in cal_calendars statt microsoft_id in Calendar
                                     $resCheckNewAttMs = $db->select("cal_calendars", "ms_user_id", "id = '" . $newAttendeeCalId . "' LIMIT 1");
                                     $hasMsId = false;
                                     if ($db->num_rows($resCheckNewAttMs)) {