VPN L2TP über LTE baut sich nicht mehr auf

Hallo zusammen,

folgendes Problem:
Wir haben iPads welche mit LTE eine Verbindung zu einem Server aufbauen sollen. Anfangs hat das Ganze auch wunderbar funktioniert, nun baut sich der Tunnel über LTE jedoch nicht mehr auf, über WLAN funktioniert das Ganze allerdings sofort. Anbei das Log über LTE:

utm-1 pluto[9531]: packet from xxx.xxx.xxx.xxx:500: ignoring Vendor ID payload [draft-ietf-ipsec-nat-t-ike-02_n]
utm-1 pluto[9531]: packet from xxx.xxx.xxx.xxx:500: ignoring Vendor ID payload [FRAGMENTATION 80000000]
utm-1 pluto[9531]: packet from xxx.xxx.xxx.xxx:500 received Vendor ID payload [Dead Peer Detection]
utm-1 pluto[9531]: "L_for a_local"[249] xxx.xxx.xxx.xxx #458: responding to Main Mode from unknown peer xxx.xxx.xxx.xxx
utm-1 pluto[9531]: "L_for a_local"[249] xxx.xxx.xxx.xxx #458: NAT-Traversal: Result using RFC 3947: both are NATed
utm-1 pluto[9531]: | NAT-T: new mapping xxx.xxx.xxx.xxx:500/21289)
utm-1 pluto[9531]: "L_for a_local"[249] xxx.xxx.xxx.xxx:21289 #458: ignoring informational payload, type IPSEC_INITIAL_CONTACT
utm-1 pluto[9531]: "L_for a_local"[249] xxx.xxx.xxx.xxx:21289 #458: Peer ID is ID_IPV4_ADDR: '0.0.0.0'
utm-1 pluto[9531]: "L_for a_local"[250] xxx.xxx.xxx.xxx:21289 #458: deleting connection "L_for a_local"[249] instance with peer xxx.xxx.xxx.xxx {isakmp=#0/ipsec=#0}
utm-1 pluto[9531]: "L_for a_local"[250] xxx.xxx.xxx.xxx:21289 #458: Dead Peer Detection (RFC 3706) enabled
utm-1 pluto[9531]: "L_for a_local"[250] xxx.xxx.xxx.xxx:21289 #458: sent MR3, ISAKMP SA established
utm-1 pluto[9531]: "L_for a_local"[54] xxx.xxx.xxx.xxx:21289 #459: NAT-Traversal: received 2 NAT-OA. using first, ignoring others
utm-1 pluto[9531]: "L_for a_local"[54] xxx.xxx.xxx.xxx:21289 #459: responding to Quick Mode
utm-1 pluto[9531]: "L_for a_local"[250] xxx.xxx.xxx.xxx:21289 #458: ignoring informational payload, type INVALID_HASH_INFORMATION
utm-1 pluto[9531]: "L_for a_local"[250] xxx.xxx.xxx.xxx:21289 #458: received Delete SA payload: deleting ISAKMP State #458
utm-1 pluto[9531]: "L_for a_local"[250] xxx.xxx.xxx.xxx:21289 #458: deleting connection "L_for a_local"[54] instance with peer xxx.xxx.xxx.xxx {isakmp=#0/ipsec=#0}
utm-1 pluto[9531]: "L_for a_local"[250] xxx.xxx.xxx.xxx:21289: deleting connection "L_for a_local"[250] instance with peer xxx.xxx.xxx.xxx {isakmp=#0/ipsec=#0}
utm-2 pluto[9819]: "L_for a_local"[250] xxx.xxx.xxx.xxx:21289: deleting connection "L_for a_local"[250] instance with peer xxx.xxx.xxx.xxx {isakmp=#0/ipsec=#0}
utm-1 pluto[9531]: ERROR: asynchronous network error report on eth2 for message to xxx.xxx.xxx.xxx port 21289, complainant xxx.xxx.xxx.xxx: Connection refused [errno 111, origin ICMP type 3 code 3 (not authenticated)]

Liebe Grüße
Chani