TBH, the first thing I'd do is just stop coasting the bike. Especially during those first 10 minutes. If the shop can't find any problems mechanically, it might well be that it's just operator error.
Modern engines with fuel injection do a very good job of cutting down on wasted fuel when you get off the throttle, so you're probably not saving much, if any, fuel by coasting the bike.
If after not coasting the bike, the problem returns, then there might be something mechanically wrong or the problem is the way in which you're rolling off the throttle. If you've got prior riding experience, then you'll likely know whether or not that's the problem. However, if you're new to riding, you might want to let off the throttle slower and more smoothly until you've mastered it.