Well it’s the same code that’s been running on that Core for literally months - I’m wondering if it might be a keys issue because the other Core that I moved down, intending to swap with the ‘faulty’ Core is doing something similar, the one I’m moving down hasn’t been powered off for a couple of months but before that was very reliable?!
It’s basically the same thing that happened to me in August 2020 - a power cut killed a Core somehow. Different error now but same net effect.