I’m no expert, but I know absorption refrigerators don’t always work well at extreme temps - although 31 degrees is well within limits. It is a very simple design that boils an ammonia solution in a small gas/electric burner. I’m guessing that the gas burner is more efficient but as I mentioned it shouldn’t be a factor at “normal” temps. I’ve used my Norcold down into the 20s on electric without problems. I think I’d wait and see if it happens again before getting especially alarmed. If it becomes intermittent on AC but alway works fine on gas you might have a loose AC connection or a quirky control board.
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