Hi, since we migrated to actor (under mw 1.31) we cannot search by users in Special:ListFiles.
Looking at the code, it's indeed incompatible with actor, see https://github.com/wikimedia/mediawiki/blob/master/includes/specials/pagers/ImageListPager.php#L137 that column is empty for me (the column is there but the value is empty and img_user is 0)