You’ve gone down the right path by having the vehicle scanned first, and even though no fault codes were revealed, that doesn’t mean it was a waste of time. In some cases, a mechanic experienced in a particular make and model will know that a fault with no code is caused by a specific part or piece of software. LS1 Holden V8s, for instance can experience a misfire with no code showing up. In that case, an experienced LS1 mechanic will go straight to the spark plugs as the cause. So the best advice is to find a Ford Transit specialist as this problem has almost certainly occurred before to somebody else. Be aware, too, that Transits built between September 2014 and January 2015 were subject to a recall to replace a batch of faulty fuel injectors which were causing the precise symptoms you’ve noted. Ford believed the problem was solved for vehicles built after January 2015 (including yours) but it’s worth checking since it was a big enough problem for Ford Australia to issue a fleet-wide recall.