Left thermistor readings are intermittent

[ARosch]

I had this exact issue a week ago, turned out to be the wire had broken right were it is zip tied to the top of the print heads. the thermistor wiring is stupidly solid copper and subject to fatigue fracturing at any point that bends the wire backwards and forwards.
on mine only the red wire had fractured/broken.

So did you just replace the entire thermocouple?