I’ve confirmed that swapping back the original ‘failed’ chip causes the updi failure again. I’m a bit concerned going back to this link that configuring the reset pin as reset rather than as gpio may have caused the problem. If this is the case, is there any way back for the chip?
I can’t use updi to check /set the fuses as the initialisation fails every time. It’s no big deal if it’s dead, but if I can resurrect it, so much the better.