Modem Locks-up with Solid Orange Light Only and Requires Factory Reset To Restore Cell Connection

We have 10+ LB1120 Modems purchased within the last year. They are all using T-Mobile SIM cards. Default settings, all powered from APC UPS's, and all running the very latest firmware/software:

Firmware: M18Q2_v12.09.163431
App Ver : NTG9X07C_12.09.05.30
Web App : LBHDATA_03.03.103.176

Three of them have exhibited an issue where they would be working fine for weeks, then at some point, we would loose connection with just a solid Orange power light only remaining. Logging into Admin page just shows Missing Internet Connection.

Power recycle does not work - this only brings you back to a solid orange light only with no service. The only thing that restores the modems when in this state is a Factory Reset. Two of the modems have continued to work after a factory reset, with the second locking up in this state again a week later. The third modem after locking up and after a factory reset, immediately connects to cell with full signal and continues to work great - until power is recycled. Once power is recycled, it comes back up to the orange solid power light with no signal bars. If you factory reset, it comes right back online - until you cycle power again, then it needs another factory reset to reconnect.

Anyone have any ideas what in the world is going on here? Is there a bug in the latest firmware rev?

a) what causes cell connection issues that forces a solid orange light and requires a factory reset to bring back online?

b) with the third modem, why does it lose the ability to connect to cell after a power cycle - but connects immediately after a factory reset - until you cycle power again?

Thanks!