I don't know....but when I had what I believed to be ghost encounters, I don't remember sensing a change in temperature.
But then again...I was freaking out so...
I've heard that ghosts do change the temperature.
The question is...does the sensor detect an increase in temp or a decrease?
I have heard that ghosts make the temp in the area of effect drop.
Having some electronic background, my next questions are...was it one sensor and how many are there in the room?
These sensors most likely have a thermistor.
If the building has had recurring problems, such as you have stated, then maybe some condensation occurred and the thermistor has been damaged in some way.
I fix helicopters for a living and there are temp gages and sensors and they usually break down after temp changes as in increasing altitude and flying into weather conditions. This snag is common.