Performance many fails?
I find that strange, it was one of the easiest subject we had when I did it. It was one of those exams you expected most to get around 100% score on.
But you are going to Groundschool for ATPL's, why are they not teaching you this properly? The Flightschool Goldwings, that you say is so great, should be able to provide you help with this. And if the answer is wrong with EASA, they should be able to get this clarified by the CAA if in doubt.
Not all QB's have the right answers, so the CAA will not tell you that the answer in the QB is wrong, that is not their duty.
They only QB I trusted was Bristol, and I tried a couple, that was less than reliable. Although long time ago now.