On a WordPress site I have a password protected directory at the same level as WordPress containing static content. WordPress is installed in the root of the site:

https://example.com/ – WordPress site

https://example.com/mydir/* – password protected files
e.g. https://example.com/mydir/somefile.txt

After authenticating, the browser can download most of the files in there but there are some that are causing a 404 response. E.g.

https://example.com/mydir/foo.txt – OK
https://example.com/mydir/foo.LICENSE.txt – 404

How I debug this?