I accidentally unplugged the USB cable from the Raspberry Pi hosting my home assistant to the Insteon PLM, and – after a great deal of troubleshooting – found that this was the cause of not being able to restart HA web interface. I had previously noticed that Insteon devices weren’t being updated in history or logs, but hadn’t put 2 and 2 together. Was about to reflash the Pi’s SD card when I found I’d pulled out the cable by dropping a bracket on it.
I could still ssh in to the Pi and check the log and see that Insteon was taking too long to start, but I would suggest that an unplugged device should produce a less fatal systemwide error. I.e., just the affected devices would not work, not an apparent total system failure when attempting to load the web interface. An unplugged insteon modem shouldn’t prevent me from seeing my radiothermostat or weatherunderground forecast or sleepnumber status . . .