Good call. The cupping effect was more of a theoretical tidbit and not the main source of a more direct reason which we haven’t found yet.
The only other underdiscussed aspect is the aspect of the temperature on the metal rod itself, but as I said, to what degree is impossible to judge from behind screens.
In any case, I hope you get it fixed, and I hope (I suspect though) that uneven frets aren’t giving you a false reading- which is why I asked about fret sprout.