When Joss Whedon came on board the Justice League movie all of the Superman scenes were reshot, but the problem was that Henry Cavill was already filming his new Mission Impossible 6 movie, which required him to have a mustache.
Paramount wouldn't allow Henry Cavill to shave for the Justice League reshoots, even though Warner Bros. offered to foot the bill to pay for the digital alterations. Instead, Henry Cavill filmed the Justice League reshoots with a mustache, which then needed to be removed through use of CGI in post-production.
As just about everybody that has seen the Justice League movie has noticed, WB didn't do all that well of a job removing the mustache.
Henry Cavill even pokes fun at the Superman mustache in the following video which he labeled with the hashtag "#ShavedButNotForgotten" on Facebook.
Mission Impossible 6 comes out July 27, and presently, Henry Cavill's calendar is pretty clear, so it remains to be seen where he will pop up next.
Check out the Henry Cavill mustache video: