Firmware update to 0004.0023.0036 - Modbus wouldn't connect - Power cycling inverter fixed it

[barrown]

TLDR: If Home Assistant has lost connection to the inverter, cut power to the inverter for ~10 seconds and then turn it back on.

Hopefully this information can help others in the future if they lose connection after a firmware update. My solaredge inverter and this modbus integration have been rock solid for years, so I was very surprised when a "fault" was detected by Home Assistant and all sensors became unavailable. I saw in the logbook that the firmware had changed from 0004.0021.0023 to 0004.0023.00036. This has never been a problem before, my inverter started somewhere around 0004.0017.0221.

Clearly the Modbus connection worked after the firmware update (because it was reported in Home Assistant) but then the connection broke and the inverted constantly refused to connect.
Checking in the installer menu by connecting directly to the inverter (http://172.16.0.1) I could see the IP and Modbus port hadn't changed, and it Modbus was still enabled as an interface. Rebooting Home Assistant had no effect. There was nothing more informative in the debug logs than the timeout errors.
Finally, in desperation, I turned the inverter off and on again using the isolator switch. "Magically" Home Assistant started displaying all the data again.