My Nitro has been having this problem for around 10 months. But it’s very intermittent and unpredictable. Like the others, you pull the big relay out in the middle and it shuts down the engine. I think it’s related to the ignition area. The key turning off isn’t shutting down the circuit. There might be dust and dirt built up in there, not sure. If ignition replacement is too costly, I’ll put a toggle switch in to shut it down conveniently.