Application Server having issues with a file within a filesystem on the NAS

Our Apps team reported an locked/unaccessible issue with a file located on the NAS They are unable to open it, they can't change permission, they can't change the owner, they can't delete or move the file. I've checked my NAS for any locks but there's no output. How can I check to see who is logged in on the NAS side? The Apps server is not showing anything on the file because they are not sure, who and what server mounted and lock the file. Will rebooting the server work or rebooting the data mover?