Klipper aborted the print with:

Heater extruder not heating at expected rate Transition to shutdown state: Heater extruder not heating at expected rate See the 'verify_heater' section in docs/Config_Reference.md

Before any of this started,I goobered my original Rapido, so I replaced it with a Rapido 2. It's been in the printer since April, but I haven't done a ton of printing with it. After the replacement, all was well for a while. At some point, Klipper started randomly tripping thermal runaway protection. The spikes were instantaneous, so I suspected a wire break. It wouldn't be my first and they're usually easy to find. I moved the tool head around trying to find it with no success. I pulled apart both cable chains (yay Voron) to look for the wire break and didn't find one. I flipped the printer updside down and connections at the MCU - everything was fine. I went through the hot end and inadvertently pulled the thermistor out of the m3 slug. Here's a stock photo:

Suspecting a potential wire break at the thermistor, I manipulated the wiring to no real effect. Inside the M3 bung was some dried white stuff, which I think was probably Boron Nitride Paste. I bought some more from Slice Engineering and reinstalled the thermistor.

Two things changed after this. First, the terminator seems to be reading lower than it did before. I say this because I have a ton more stringing than I did previously. Second, the temperature is no longer spiking but it is doing this high frequency oscillation thing now.

The oscillation only happens once the printer is moving quickly. If it's still, or moving slowly, things are fine.

Thoughts? I'm suspecting the thermistor, but would like to troubleshoot if possible vs just throwing parts at the printer.