MR1100 Connected via LTE but stops routing internet after some period of time

Recently picked up an MR1100 router. The first few weeks it seemed to work okay. Suddenly, after some random period of time (usually between 1-18 hours), the device will stop routing internet via Ethernet and WiFi. This affects all devices (Windows PCs, Macs, and iOS).

The WiFi connections are fine and logging into the router shows that mobile broadband is "Connected". Looking at the connection time will show there was no disconnect (often see it at 16-18 hours when the failure occurs). My signal strength typically shows as "Good" or "Excellent".

I have tried this across multiple SIM cards and providers (T-Mobile and AT&T with true hotspot / router plans). The issue still occurs on all SIMs and networks. I am still able to ping public IPs and resolve DNS. TCP connections seem to fail, though. It's as though the router just stops routing, even though there is an active cellular connection.

I can even force the LTE data connection off and back on. The router disconnects and reconnects to the cell network. But internet never functions again. The only resolution is to pull the plug on the router and plug it back in (rebooting from the web UI causes the router to lock up and not respond to the button on the side of the device).

This has unfortunately made this device unusable for me. Currently looking for a more reliable device. Would be great to fix this or at least understand what the issue is, though.