Sounds like the one thermocouple may have been damaged. I mounted an experiment in the ATR and one of the thermocouples showed significant drift compared to the others. I think it was a radiation effect on the thermocouple junction, although we never did any PIE to precisely determine that.
Well!
As a former factory tech that info makes me think it was shifting debris.
Typically, when we did something-like remove that pump- whatever changes was caused by what we did... somehow!
Thermocouples I’m familiar with are easily changed out .
Though there could be concern that the well is punctured- or some other issue- could prevent it here of course (seems a simple task for a robot if radiation is the problem).