Hello,
I am not able to check Network Admin settings using access from the private content area.
Please check “Upload file types” one more time – http://prntscr.com/mtiepp if this doesn’t help, add this code in functions.php your child theme:
function my_custom_upload_mimes($mimes = array()) {
// Add a key and value for the CSV file type
$mimes['csv'] = "text/csv";
return $mimes;
}
add_action('upload_mimes', 'my_custom_upload_mimes');
and try to upload the desired file one more time.
Please note that we are theme support and are able to help with problems strictly related to our theme only. In your case, when the problem persists with the default theme too, I would recommend you to contact WordPress support.
Let us know if you need any other assistance.
Regards