Alarm Panel 2 Add-on will not reboot

I have a Alarm Panel 2 board and a Alarm Panel 2 add-on board.    The Add-On board has dropped the Wifi connection, and will not reboot when I press the onboard reboot button.   Indications: the blue connection LED comes on for about a tenth of a second just as I press the reboot button.   The unit is not apparently trying to connect with wifi.   I don't know what caused the unit to drop the Wifi in the first place, so that is certainly a concern.

Any suggestions on how to force a reboot (other than cycling power, which I will do as a last resort)?