It’s best for all the WordPress files on a Linux based OS to have the same owner and group (for example wpadmin:wpadmin). Also, the file permissions should be 644 for files and 755 for folders. Depends of course on the server setup you have, however, those are the most common ones.
In your case, I believe the problem is the server. I don’t think this is something related to WordPress. I would advise you to check the configuration of the Apache you are running ??
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