How many hours are on that deck? It could be that there just needs to be an adjustment that is due after so many hours.
Other than that, some tapes just don't work that well in ADAT's. Like Ampex S-VHS!!! That stuff is junk and kind of expensive. I exclusively use Maxell Professional Grade S-VHS tape and have never, ever, ever had any problems at all with it. I have had all sorts of problems with Ampex S-VHS tape; faulty time code, eaten tapes, broken tapes at the back end, etc......
So, if your deck has less than 1000 hours on the head stack, then you might consider another brand of tape. If neither is the case, then your ADAT may need a servicing.
Good luck.
Ed