****!, Drink!, Girls!
Have you checked all the electrical connections live, neutral, and earth's from the main house D/B through to the.welder outlet?
Could be a loose terminal, I've had this at work when something works fine one minute then goes screwy the next. Worth a check as it might save your house burning down.
Can do it, seems odd though as i would think the lights and CNC stuff would be going mental. I'll do some checks though, I know the workshop panel is ok as i was in there last week and tweaked all the clamps as a matter of course. I'll check the house end joints.
It does seem to do it more if i don't use it much - been used pretty much every day these last few weeks and not done it at all. That makes me think of a gas leak maybe??
The line to the welder seems tight as it will hold pressure for weeks, maybe line from unit to tip??