I used the WE826 quite often in the past. Did not know, there was a HW-watchdog. Pls, provide details about it.
On other systems, MWAN3 is sufficient to dyn switch between wan/wifiwan/wwan on a RUT955 (Teltonika). However, I added custom script, to periodically check web connectivity, and powercycle the modem , or , in worst case trigger a (software-)reboot, in case no web connection for minutes. Until now, this was sufficient in many installs, besides very few exceptions. However, I was already condsidering an external watchdog (special hardware device), to externally power-cycle the router in very last case. You might consider this option, which MUST work, because your manual power cycle fixes the problem.