Could do with a little help here as I'm really stumped.

Okay, for the new problem… Is it an ATX style power supply? Those have one set of wires that I believe can power off the power supply if they run low or some such thing. How long have you used the board that is in there right now? Try swapping it out to test if it is the board?

Standard LED PSU, switched via a SSR for use of M80/M81. RAMPS/Arduino has been in there since I built the first FB2020 7-8 months ago, admittedly, the RAMPS was cheap. Basically, something is shorting somewhere just after a print begins, runs through the start GCode then as soon as it moves to start the skirt it just resets.

Mice/cats/insects?

None of the above…

Do you have a crimp job that missed a strand or two of copper that is now hitting another connector? I had that problem with wires on my CNC machine a couple of times.

It’s possible. I’ll take a look at it later on.

So, I’ve got the 2nd issue fixed. Seems I had something configured incorrectly for my setup in Marlin RC8 that didn’t like S3D’s sliced files for single nozzle setups. I’ve no idea what and sliced the same file with Mattercontrol and all was fine, possibly something to do with the M4 dwell, can’t say, but I’ll take a look on the Marlin Github. I’ve jut rolled back to RC7 and all is printing fine and dandy…