Hello m8
I had same kind of problem on my st. Turned out to be a faulty cps. The sensor is still available from ford, did not cost many euros. Easy to change, just loosen one pinchbolt and slide the sensor out of its bracket. The bracket is situated at the front end of the crankshaft/oilsump. The heat coming from the sump/engine via the bracket cause the sensor to fail. Can easily be verified by cooling the sensor with compressed air when the fault occurs. If it stars after short period of cooling, thats the problem. Hope you find the problem, and whats causing it.