After flashing the router, same symptoms. Connected in a few seconds over /dev/ttyusb3, data transmitted for about half an hour, after that I lost connectivity for several minutes. During that time there was an error message “SIM not registered” displayed in the modem box.
EDIT: After looking through the forum this issue appears similar to the issue brought up: here. Slightly different symptoms but the same effect & modem. Ran the same AT commands, responses below in case they’re helpful:
AT+CREG?
+CREG: 0,0
OK
AT+QNWINFO
+QNWINFO: "FDD LTE","311990","LTE BAND 12",5145
OK
AT+CEREG?
+CEREG: 0,1
OK
AT + CGREG?
ERROR (response successful)