We have a beer fridge in the basement and I keep store bought ice and some of those bags you freeze in it. There is a thermometer in it and it has started giving varying readings. Usually it is very cold, but once in a while it will be higher near the freezing mark.

It is an old fridge and the fridge part seems to be ok.

what about a old leaking door gasket which could be the changing of temperatures /coils need cleaning......parents had a door gasket replaced with a generic gasket when orginal failed at 50 yrs ...............drill sgt.

Are you catching it during an automatic defrost cycle?

My guess would be the thermostat. But it's purely a guess. How old is the unit?

Could be a bad damper?

Is it a self defrost? Is warmest temp the same time each day? If so probably in defrost mode.

Your timer could be going and it's staying in defrost mode longer than it's supposed to. It's a pretty easy fix.