wifi75 And still same result from the test script, dir is not readable? That could imply that it's the actual server (Apache/Nginx) that is not allowed to access the dir.
Perhaps try to create a symlink in your server document root, and point it to the mounted dir, and then try to access the symlink from browser? This would let you know if the file(s) are accessible from the web server, unrelated to PHP.
As long as PHP is_readable()
returns false
, it means the dir is not readable by Files Gallery.
I have to go now, back later ...