So yet a further option then: not a temperature-related read error, but some kind of residual charge issue or so that causes a read error absent sufficient time or cooldown to reset.

That makes me think of this:

where @CFSworks deftly showed how it is possible to store a value in RAM that survives warm reboots and can be checked for via checking a RAM-backed mtd device.

Could it be that there is some kind of reset line or function that needs to be called between reboots to clear any such residual charge issues?

Ah - frustrating. Since this seemed to me promising in terms of a possible explanation for the issue given thef documents I identified about read disturb:

And the first paper disclosed various techniques for mitigating like tweaking Vpass:

And calibration: