incubator mechanical help please

I have a hovabator still air incubator - the styrofoam thing with the wafer for a thermostat.

I've not been having problems with the temps at all. I've been watching closely and adjusting, and the past two days, it has been perfect, right on the mark.

I got up early this morning and turned the eggs before leaving to go do laundry. I admit i didn't look at the temp this morning because it was dark. But when i got back a couple of hours later and checked the temps, it was down 4 degrees, and the light was on like it was still warming. I checked around to make sure the lid wasn't caught on anything (it wasn't) and jiggled the thermostat thing a little just in case something was amuck there. I left it for a few more minutes and the light finally went off, but the temperature was still low. So i turned it up.

Here's my question i guess, since i don't really understand the mechanics of the wafer doolihopper.

Does my lifting the lid off and on to turn the eggs mess up the mechanics of the thermostat? I don't understand why temp would be perfect for several days and then suddenly low, without having adjusted the thermostat.

Also, yesterday i candled and then removed 3 eggs (total down to 45). Could the removal of 3 eggs affect the temps that much?

Thanks for any enlightenment. This is my first time.