In my case, I just needed to refresh the page. Sometimes the progress seems to be stuck on the frontend, but I believe the scan process is still running on the background.
Check your PHP error log, something might be there. I guess a part of the execution takes too much time (or memory) and PHP stops.
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.
Again, PHP logs, or open your Chrome Developer Tools and check what the reply from the server was, the error would show clearly there.
Please post issues here:
https://github.com/tigroumeow/wp-media-cleaner/issues
But it needs to be descriptive and debugged.