Hi we run a fleet of vauxhall Movanos () and had the same kind of fault a few times now and it has come down to the crank sensor / wiring plug not being on all the way, I have just put a cable tie around it to hold it in place and touch wood I havent had a problem with any of them (but it took some finding it the first place!!!!). Hope this helps cant say it will be it but it has sorted 3 for me.