There's stories doing the rounds about his behaviour on the Justice League reshoots (apparently it wasn't just Ray Fisher, he was also rather nasty towards Gal Gadot and a dick towards Jason Momoa - the latter explains a lot as I believe he was one of the first cast members to come out in support of the Snyder Cut) as well as stuff he's worked on in the past.
The one that somehow escaped me in the time since the show finished, was his treatment of Charisma Carpenter, basically for having the fucking nerve to get pregnant during filming of Angel.
https://www.distractify.com/p/joss-whedon-charisma-carpenterThe one thing that kept coming up when I searched this last night was that when Carpenter had given birth and was ready to comeback to the show, she was basically lied to about how her role on the show going forward. She had one of the best arcs across Buffy and (especially) Angel only to be killed off out of spite, essentially.
Then there's all sorts of gossip-y shit that I ended up reading last night, some of which, if actually true, would explain a lot. You can google that stuff yourself if you want.
Basically now, in my mind Joss Whedon has somehow become worse than Graham bloody Linehan, in that its harder to separate Joss from Buffy, Angel and Dollhouse (fuck Firefly, though), than it is Glinner from Father Ted/Black Books.