I see; though, a thermistor not making good contact with the heat block would imply the heat block is hotter than reported, not the other way around.
This glass thermistors are a nightmare. I kept accidentally ripping the leads off mine. During this whole debacle, I treated myself to a fancy thermistor that is built into the end of an M3 bolt - it screws in to the hole meant for the grub screw that normally keeps the glass ones in place.