I have the same problem. If I scan the uploads folder I only see the “Please wait” info and get an debug error Uncaught SyntaxError: Unexpected token </wp-admin/upload.php page=wp-media-cleaner line 1
If I check the media library it stops at 5/1120 (0%) I get Uncaught SyntaxError: Unexpected token </wp-admin/upload.php?page=wp-media-cleaner&reset=1 line 1
Tried to change timeout in php.ini to 0. Did not help.