Ray Fisher's issue (that was confirmed by his co-stars including Gal Gadot who played Wonder Woman and Jason Momoa who played Aquaman) was that Joss Whedon was abusive to the actors on set and had some
tendencies.
In Snyder's film Cyborg was the emotional heart of the movie but when Whedon came in he cut almost all of the Cyborg stuff.
Also the people who were in charge of the DC movies at the time were desperate to get some of that Marvel movie shine which is why they hired Whedon in the first place (he made the first 2 Avengers movies) and they gave him the greenlight to "Marvel up" the movie Snyder had shot. So Whedon cut and re-shot the bulk of Snyders movie.