update header if start / end date changed / an activity deleted

app/Models/Activity.php

@@ -63,7 +63,7 @@ class Activity extends Model
 				$data->updatePersentaseProgress();
 				$data->updateCostActual();
 			}
-			if($this->start_date != request()->start_date || $this->end_date != request()->end_date) {
+			if($data->start_date != request()->start_date || $data->end_date != request()->end_date) {
 				$data->updateStartEndDateHeader();
 			}
 		});