When it was announced that Zack Snyder had left the Justice League project and that there were going to be some big reshoots, it was always going to be interesting to see what would happen with Henry Cavill, since he was growing a moustache for his role in the new Mission Impossible movie, and Superman does not have a moustache in the Justice League film.

Warner Bros. attempted to persuade Paramount to allow Henry Cavill to shave his moustache off, even offering to add a CGI moustache to the Mission Impossible movie for them. Paramount did not agree to this, so the moustache had to stay, which meant that they would have to use CGI to edit out the moustache in Justice League, which did not work well at all.
Cavill has now said, "When we decided to go for the moustache, I certainly wasn’t expecting all the events to unfold as they were going to unfold. I wasn’t expecting Justice League reshoots to be as extensive as they were. When it came to that, it was one of those things where I’m in the middle of another movie, and to change my look for a movie that should have finished already becomes a real problem."

He added, "And as you will see when the movie comes out, to have a fake moustache on would not have been a possibility. You’ll think, ‘Okay, yeah, a fake moustache would perhaps have been blown off in this situation.’ Unfortunately, it led to much dismay when Justice League came out, but that’s the nature of these things. You can’t win every time."
We are not sure when we will see Henry Cavill back as Superman on the big screen but we are definitely looking forward to him not having that moustache.