STC1000, temp up and down in keezer?

I have had a stc1000 on my ferm fridge for a long time, and it works great. Its in an external box. I keep the probe taped to the side of whatever is fermenting, insulated by a 3" chunk of paper towel.

I made another box to run my keezer, and it worked fine. Temps did not seem to swing very much. I keep the probe taped to a keg, insulated by a 3" square of paper towel.

I have now integrated the unit into the keezer collar, so the unit is basically inside the keezer. It is still taped to the keg as it was before, but now it seems very sensitive to temp swings when I open the keezer lid. I have no idea why this would be, its still insulated and taped to the keg just as it was before. For example, just tonight - the unit was reading 3.4 C. I opened the lid to pull a carboy out (Literally, 30 seconds?) and the temp rose to 9 c. Its hot out today, but c'mon!

Am I losing my mind? Would the unit being exposed to cold air now make a difference? What about the probe lead wires, the ones that get tightened into the unit, could they cause funky fluxes?

I'd upgrade your probe insulation to something more substantial than a square of paper towel, but even so, 30 seconds seems way too quick for that large a temperature delta. I would check all the connections at the back of the controller, hopefully one of the probe leads isn't tight. Otherwise, check how the probe wire flexes with the lid movement, perhaps you're working up to a fatigue failure...

Cheers!

I will upgrade to a better insulator and double check the connections. The probe wire is inside the keezer and is not in contact with the lid at all.