I have lots of 819 routers with the same problem. When there is a problem with primary GSM operator router reconnect to secondary GSM operator. Sometimes something will happen and it doesn't connect to any and hang.
I try to made reload event with sla and track but track delay is limited to 180 sec. and sometimes router has no enough time to connect to Internet after start and made cycle reboot.
Heave you any idea what I could do?