Frustrating! I think you are wise to take it in again.
Your machine is like me a night owl :o)
Tell them in the shop that they should try it at the same time or more than only once. Had the same with a car and they only found the fault cause I said the mechanic should take my car instead of his own and use it for the next days. Right on his way home the car acts up and they found the problem then.
Greetings, Bettina
Hopefully it will be fixed soon. It is actually working. Just that the problem will not go away by itself.
DON'T YA JUST HATE THAT? Good luck with it all, love Chris