WAN port was connected all time. So my first FW-upgrade to 7.01.2 was OTA.
What I've done in meantime was reflashing with FW RUTX_R_00.07.01.2. After that mobile connection worked well, maybe due to settings cleared because of downgrade.
After your comment I upgraded again to 7.01.2 with WAN connected. The problem persists even after a full factory reset. The "Modem occupied by FW update..." messages are appearing for over 20 minutes. Mobile connection seems active (traceroute -i wwan0 ... worked). When applying changes to wwan interface (set apn) " Failed to execute AT command: AT+CPIN?" and the "modem occupied..." messages continue. After reboot "modem occupied..." continue every 10s.
Modem status reports "connected", but state and bytes received N/A and SIM not inserted. However mobile data connection seems to work.
Do you have any advice to solve this issue?