I had the issue once on my Max and traced it down to the wires going to the main switch to be unsufficiently tighten.
There is on the top screw the main wire and at the bottome eight or nine wires coming toegether on a screw. These are covered with some form of loctite
The wires moved a bit and provided loose contact.
I took the loctite out and could tighten the bolt by over eight turns
That is a very poor engineering, such a loose connection is a design fault
