I have seen where the seat switch is not adjusted properly or not fitting in its retainer properly and a bump that causes you to shift your weight on the seat is just enough to cause the safety switch to open. Can't say for sure if that's your problem but I've seen it before. Possibly heat causing the clutch coil to go open? You'll have to make a few checks when the problem is evident to find this one.
I run one of these been having this problem. Cutters will automatically cut out when engine overheats. Clean screen on radiator every day and keep coolant level up
