Sounds like one of the probes is being messed with by the heaters.one at the beginning of the sump and one at the end. The ambient temp and sump being a cooler makes since. my sump is in my basement and its cooler down the obviously. I guess I’ll have to get a space heater?
Try move both probes to the compartment with the filter sock and see if issue persists.
You don’t want one, or both, taking readings from freshly heated water. The compartment with the filter sock should, assuming you have vaguely decent flow in the tank, be close to the temperature in the tank.
If this does not resolve the issue try using the heaters to heat a 30 gallon bucket of water (assuming you have one for water changes) and see if they’re actually working. Last I had issues with heaters not heating it was because one wasn’t, well, heating anymore.