I'd bet the flash dropped a bit or two somewhere. Reprogramming it fixed it.

We've have flash chips do similar things and then come good once reprogrammed. We've had them sometimes give a 1 and sometimes a 0. Once reprogrammed they worked fine for a while (years). The manufacturer did finally acknowledge a problem with these particular once. Maybe the heat just made it a bit worse. Remember flash memory is technically not non-volatile. It has the potential to lose bits over time. Normally we are talking tens of years, but heat is very likely to accelerate that.

Doesn't explain why the disk builder wouldn't go on though.