It could be a loose wire, or a one that is about to snap off. If the cable is bad or on the way out, it could easily be screwing with the resistance measurement. I wouldn’t think that just a loose thermistor could cause that mess of a graph, but who knows.
It’s the motion bit that you mentioned that gave us just a little more data.
If you can isolate the wire for the thermistor, jiggle it around at different points to see if you can replicate the rapid temperature changes.
It could be a loose wire, or a one that is about to snap off. If the cable is bad or on the way out, it could easily be screwing with the resistance measurement. I wouldn’t think that just a loose thermistor could cause that mess of a graph, but who knows.
It’s the motion bit that you mentioned that gave us just a little more data.
If you can isolate the wire for the thermistor, jiggle it around at different points to see if you can replicate the rapid temperature changes.