As I said, there are teething problems with things like the drivers not releasing the doors quickly (it took drivers a while on TL to get good at this, and in some cases there were other issues like the positioning of stop boards etc). The same issues can be at the prep stage, meaning a train comes out of a yard/siding late.
I wouldn't say it's poor training, but when you're going through a LOT of drivers to get them all capable of driving 700s, there's a chance that when they go out for the first time in passenger service they're going to forget the odd thing as there may not have been time to go beyond the training and give tips and tricks.
They'll then need to call for advice, which takes time. With the problems of late, a train dealing with a door issue (which doesn't mean the train has failed) could see stations skipped, or even the service being cancelled altogether.
These issues will go once the GN drivers are not only authorised to drive them but also build up a knowledge to do their own fault finding and fixing.
I'll stand corrected if there are faults I am not aware of. This week some trains have been short formed (8 cars instead of 12 cars) because some trains were in the wrong places. I don't think it was down to units being repaired. Again, I'll stand corrected if I am wrong.