Multiple women have accused him of sexual harassment, including someone who says she was 17 at the time. Ty Franck and Daniel Abraham, the authors of the novels under a joint pseudonym who are also producers of the show, Tweeted from their pseudonym's account that the studio, Alcon Entertainment, had hired an independent third-party investigator to look into the allegations. We heard no other updates on that until it was announced yesterday that Anvar is not returning.
Seems probable to me that the investigation demonstrated that at least some of the allegations were legit.