I believe the drivers for that system was produced by the manufacturer, so it would be up to them on how to handle things if the boards are unreachable.
Take one of your boards offline and then go to the device page for it.
Make note of the "Last Activity" timestamp (on info tab for 2.4.0)
Then try running refresh or some sort of command that it should respond to (anything except configure or initialize).
Then check the Last Activity again, has it updated to current time or is it still the old time?
If Last Activity does not update when the board is offline you can use [RELEASE] Device Activity Check - Get notifications for "inactive" devices to monitor it and check once a day to see if it is online or not.
Another option would be if you have any sort of NAS or server that could run Docker, would be to setup Uptime Kuma and setup some ping checks for the boards. This would give you a much faster alert if they go offline from the LAN.