So after more then 67h the gateway hangs again. This is the debug output:
(di 01-09 09:58:49.398) 243740964 RFM69:SWR:ACK,FROM=31,SEQ=60,RSSI=-98
(di 01-09 09:58:49.398) 243740969 THA:SND:MSG LEN=9,RES=1
(di 01-09 09:58:49.398) 243740974 TSF:MSG:SEND,0-0-31-31,s=2,c=2,t=3,pt=0,l=2,sg=0,ft=0,st=OK:11
(di 01-09 09:58:49.585) IC<CR>
(di 01-09 09:58:49.585) IH<CR>
(di 01-09 09:58:49.585) 243741189 THA:DATA:AVAIL
(di 01-09 09:58:49.641) 243741241 RFM69:SAC:SEND ACK,TO=31,RSSI=-71
(di 01-09 09:58:49.703) 243741246 RFM69:CSMA:RSSI=-100
(di 01-09 09:58:49.703) 243741253 THA:RCV:MSG=1F1F000A2103020B
(di 01-09 09:58:49.703) 243741256 THA:RCV:MSG LEN=8
(di 01-09 09:58:49.703) 243741261 TSF:MSG:READ,31-31-0,s=2,c=1,t=3,pt=1,l=1,sg=0:11
(di 01-09 09:58:49.703) 243741268 GWT:TPS:TOPIC=ms-rfm-from/31/2/1/0/3,MSG SENT
(di 01-09 09:58:49.703) IC<CR>
(di 01-09 09:58:49.703) IH<CR>
(di 01-09 09:58:49.703) IC<CR>
(di 01-09 09:58:49.703) IH<CR>
(di 01-09 09:58:49.703) 243741282 THA:DATA:AVAIL
(di 01-09 09:58:49.733) 243741334 RFM69:SAC:SEND ACK,TO=31,RSSI=-68
(di 01-09 09:58:49.737) 243741339 RFM69:CSMA:RSSI=-96
(di 01-09 09:58:49.742) 243741345 THA:RCV:MSG=1F1F000A21030A0B
(di 01-09 09:58:49.747) 243741349 THA:RCV:MSG LEN=8
(di 01-09 09:58:49.752) 243741354 TSF:MSG:READ,31-31-0,s=10,c=1,t=3,pt=1,l=1,sg=0:11
(di 01-09 09:58:49.759) 243741361 GWT:TPS:TOPIC=ms-rfm-from/31/10/1/0/3,MSG SENT
(di 01-09 09:58:49.766) IC<CR>
(di 01-09 09:58:49.767) IH<CR>
(di 01-09 09:58:49.862) IC<CR>
(di 01-09 09:58:49.862) IH<CR>
(di 01-09 09:58:49.911) 243741466 THA:DATA:AVAIL
(di 01-09 09:58:49.915) 243741518 RFM69:SAC:SEND ACK,TO=31,RSSI=-69
(di 01-09 09:58:49.921) 243741523 RFM69:CSMA:RSSI=-97
(di 01-09 09:58:49.926) 243741529 THA:RCV:MSG=1F1F000A21171642
(di 01-09 09:58:49.978) 243741533 THA:RCV:MSG LEN=8
(di 01-09 09:58:49.978) 243741538 TSF:MSG:READ,31-31-0,s=22,c=1,t=23,pt=1,l=1,sg=0:66
(di 01-09 09:58:49.978) 243741545 GWT:TPS:TOPIC=ms-rfm-from/31/22/1/0/23,MSG SENT
(di 01-09 09:58:49.978) IC<CR>
(di 01-09 09:58:49.978) IH<CR>
(di 01-09 09:58:59.817) IC<CR>
(di 01-09 09:58:59.817) IH<CR>
(di 01-09 09:58:59.881) 243751420 THA:DATA:AVAIL
(di 01-09 09:58:59.881) 243751473 RFM69:SAC:SEND ACK,TO=31,RSSI=-71
(di 01-09 09:58:59.881) 243751478 RFM69:CSMA:RSSI=-100
(di 01-09 09:58:59.881) 243751485 THA:RCV:MSG=1F1F000A21171643
(di 01-09 09:58:59.909) 243751488 THA:RCV:MSG LEN=8
(di 01-09 09:58:59.909) 243751493 TSF:MSG:READ,31-31-0,s=22,c=1,t=23,pt=1,l=1,sg=0:67
(di 01-09 09:58:59.909) 243751500 GWT:TPS:TOPIC=ms-rfm-from/31/22/1/0/23,MSG SENT
(di 01-09 09:58:59.909) IC<CR>
(di 01-09 09:58:59.909) IH<CR>
(di 01-09 09:59:09.771) IC<CR>
(di 01-09 09:59:09.771) IH<CR>
(di 01-09 09:59:09.771) 243761374 THA:DATA:AVAIL
(di 01-09 09:59:09.860) 243761427 RFM69:SAC:SEND ACK,TO=31,RSSI=-70
(di 01-09 09:59:09.907) 243761432 RFM69:CSMA:RSSI=-101
(di 01-09 09:59:09.907) 243761439 THA:RCV:MSG=1F1F000A21171644
(di 01-09 09:59:09.907) 243761442 THA:RCV:MSG LEN=8
(di 01-09 09:59:09.907) 243761447 TSF:MSG:READ,31-31-0,s=22,c=1,t=23,pt=1,l=1,sg=0:68
(di 01-09 09:59:09.907) 243761454 GWT:TPS:TOPIC=ms-rfm-from/31/22/1/0/23,MSG SENT
(di 01-09 09:59:09.907) IC<CR>
(di 01-09 09:59:09.907) IH<CR>
(di 01-09 09:59:11.447) MQTTP topic
(di 01-09 09:59:11.578) ms-rfm-to/31/2/2/0/3<CR>
(di 01-09 09:59:11.578) 243763051 GWT:IMQ:TOPIC=ms-rfm-to/31/2/2/0/3, MSG RECEIVED
(di 01-09 09:59:11.578) 243763059 THA:SND:MSG=00001F120203023132
(di 01-09 09:59:11.578) 243763065 RFM69:SWR:SEND,TO=31,SEQ=65,RETRY=0
(di 01-09 09:59:11.578) 243763072 RFM69:CSMA:RSSI=-98
(di 01-09 09:59:11.578) IC<CR>
(di 01-09 09:59:11.578) IH<CR>
(di 01-09 09:59:11.578) IC<CR>
(di 01-09 09:59:11.578) IH<CR>
(di 01-09 09:59:11.578) 243763088 RFM69:SWR:ACK,FROM=31,SEQ=66,RSSI=-96
(di 01-09 09:59:11.578) 243763092 THA:SND:MSG LEN=9,RES=1
(di 01-09 09:59:11.578) 243763097 TSF:MSG:SEND,0-0-31-31,s=2,c=2,t=3,pt=0,l=2,sg=0,ft=0,st=OK:12
After this, nothing happens anymore. I'm out of ideas...