Even though I win matches, I can't get trophies in the players' league
Same. There is a bug for over a month now. (At start it was this “league not full”)
you need to “leave league” and join a new one and it fixes it. You will start with zero points of course.
The bugs are different though the most recent one may be related to fixes to the first one. Leaving leagues won't help with the current one, unless you're not in any division at all, where it might.