I think there is a bit of confusion here between the title of the thread: basically, I have possession but less shots/opportunities than my oppo and I lose. This is perfectly normal and happen very often. Possession is driven by midfielders, home game, bonus and friends. You may well have possession and be destroyed by your oppo counter-attacks.
The other discussion is: I used to be unstoppable and now I lose. This happend to me some 10 seasons ago. I was by miles the best team, the others did not even bother attending and still, I was losing. Just blame it on a run of bad form. Because in my case, I just changed nothing and suddenly became unstoppable. So be patient would be my advice.