Well, mainly because I don't know much!
Motorhome parked at the house plugged into electric service to exercise the various things. One of them being your standard Dometic 2way refer. So I turned refer on that night and checked it the next day, nice and cold.
So that day I left refer on and unplugged from the electric service for a couple of hours then plugged back in that night. Checked on the refer next morning and not cold.
While still plugged in, turned refer off and back on that evening. Checked refer the next morning and nice and cold.
So I learned that if the electric service is interrupted, it's best to turn refer off, make sure you have electric, and turn it on.
Maybe I need to read the manual