JK's Harry Potter books started out pretty tight but as the series went on, the books got longer and longer and got bloated, to me. It seemed like nobody was in a position to edit the works and rein things in (I don't know that's the case, that's what it felt like).
Then, she was vey involved in the Fantastic Beasts movies, screenwriting the first two, and co-writing the third. I can imagine a situation where there was just no pushback or questioning going on.
And aspects that may have seemed charming and endearing in script form (like a bookish, mumbling, quiet-talking lead character) didn't translate to a strong on-screen lead. Maybe people with more experience making movies would have anticipated that (Indiana Jones managed to be bookish but a whole lot more as well). Maybe there was nobody who could caution JK on that or much else. But the result was painfully unwatchable for me.
The only reason I even tried was the series' relationship with the Harry Potter stories. If you take that away, and this series was stand-alone, yikes.