Could it be because I’m using a PP that is designed to run without a THC?
Doubtful, the port won't know a plasma cutter form a mill - its just a port.
After the cut, there should be an M05 which turns the torch off, then a G00 Znn where nn is your clearance height.
The clearance height is relative to the height by your probing routine, if the probing works, then the torch tip should return to clearance height after every cut.
Any chance you can show some code?