No. I’m not using proxy.
I’m now going through the second link.
I’ll keep you posted.
[update 1]
This post seems to help:
I’ve change Header set to Header always set for the two X-Content-Type-Options and X-Frame-Options in .htaccess. Error messages are gone now. I know this is not preferable, but I’m the only one using this instance of NC.
I still do not know where the DENY option is coming from.