The problem is in your seat.
Bear with me on this..
So earlier this year I took my own seat off to lube the inner workings of the seat. When I put the physical chair back on, I failed to notice 2 metal tabs that must be inserted into 2 specific holes in the FRONT of the physical seat.
This ended up with a situation where the seat was setting *on top* of the tabs. I had no indication anything was wrong when I bolted everything back in place.
When I sat on the seat, it was just enough to push down the kill switches. However, OCCASIONALLY when I took a corner, the unit would die. My weight would shift in just the wrong way.
I realized you said the unit only cuts out with the PTO engaged, but my hunch says that has just been a coincidence.
I'm assuming you and the dealer have already checked the logical, like pinched wires and such.
My gut says the metal tab on one side is in properly, but not on the other side.
If you want to confirm this before digging in, recreate the problem and try to get a view of the TCM under the hood before you move. If I'm right, the "Seat Switch" will be lit up. You may need a mirror on a stick, or your cell phone and some putty, or a helper who can safely approach once the engine is dead.
