I had a power cut of 1 hour. After power returned my Garagdet was reporting an error. The only way I could get it to work again was to push the M button for 5 seconds and go through the initial set up again. Does it not have non-volatile memory?
There must be some other factor at play. WiFi credentials and device settings are stored in non-volatile EEPROM memory.
Did you try “R” button or power down first? The rest of the network infrastructure has to be booted up for the (re-)connection to be successful.