diff --git a/lib/Controller/SignalingController.php b/lib/Controller/SignalingController.php
index 9902e27deec..c6b26c7cfc8 100644
--- a/lib/Controller/SignalingController.php
+++ b/lib/Controller/SignalingController.php
@@ -547,6 +547,14 @@ private function backendRoom(array $roomRequest): DataResponse {
 				try {
 					$participant = $room->getParticipantBySession($sessionId);
 				} catch (ParticipantNotFoundException $e) {
+					if ($action === 'join') {
+						// If the user joins the session might not be known to the server yet.
+						// In this case we load by actor information and use the session id as new session.
+						try {
+							$participant = $room->getParticipantByActor($actorType, $actorId);
+						} catch (ParticipantNotFoundException $e) {
+						}
+					}
 				}
 			} else {
 				try {