I cannot access PDF files uploaded in the private directory

Question

PDF files uploaded to the private directory cannot be viewed and returns a 404 error. This also happens to the user with the Administrator role. Other file types can be viewed with no issue. This issue happens in a production environment, hosted on Cloudways, where the private directory is set from the following line in the settings.php file.

$settings['file_private_path'] = $app_root . '/../private';

Steps to reproduce

• Login to site as administrator user (the one with the Administrator role)

• Add a file field to the Article content type

• Set its Upload destination to Private files

• Set Allowed file extensions to txt, pdf, doc, docx and Maximum upload size to 1 MB

• Set the file directory to article-test (When the server root directory is public_html/web, private files should be uploaded to public_html/private/article-test.)

• Create an Article node and upload a valid PDF file whose size is less than 1 MB (doc_0.pdf)

• Save and publish the node

• View the new node

• Click on the file link for the uploaded file, which links to https://<domain>/system/files/article-test/doc_0.pdf)

• The site returns a 404 error

• The browser bar shows https://<domain>/user/login?destination=/system/files/article-test/doc_0.pdf as URL

• Go to https://<domain>/admin/content/files

• Click on the file link (https://<domain>/system/files/article-test/doc_0.pdf)

• The site still returns a 404 error

• The Drupal log shows page not found Location https://<domain>/user/login?destination=%2Fsystem%2Ffiles%2Farticle-test%2Fdoc_0.pdf

• Remove the uploaded file from the node

• Upload a text file or a Microsoft Word file

• Viewing the file doesn't return any 404 error

• viewing the file, a prompts ask for saving or viewing the file

I don't believe this is a permissions issue; otherwise, I wouldn't be able to access these other file types.

The file permissions for the public_html/private directory and its directories are set to 775. The file permissions for the uploaded files are set to 664.

Is there a setting (PHP, Drupal, or server) I should change to allow the PDF files to be viewed?

There is an .htaccess file in public_html/private directory. Thinking it may be related to the issue, I temporarily renamed it to .htaccess.saved. I then tried to access the uploaded PDF file, still obtaining a 404 error.

One more fact: If the same exact PDF file is uploaded to the site's public directory, the file can be viewed without errors.