Setup & security warnings behind nginx proxy

I’ve had ownCloud working behind an Nginx proxy via the Docker image for a year or more, but I noticed today that the Settings -> Admin -> General page is showing these:

This server has no working Internet connection. This means that some of the features like mounting external storage, notifications about updates or installation of third-party apps will not work. Accessing files remotely and sending of notification emails might not work, either. We suggest enabling the Internet connection for this server.
The "X-XSS-Protection" HTTP header is not configured to equal to "0". This is a potential security or privacy risk and we recommend adjusting this setting.
The "X-Content-Type-Options" HTTP header is not configured to equal to "nosniff". This is a potential security or privacy risk and we recommend adjusting this setting.
The "X-Frame-Options" HTTP header is not configured to equal to "SAMEORIGIN". This is a potential security or privacy risk and we recommend adjusting this setting.
The "Strict-Transport-Security" HTTP header is not configured to at least "15552000" seconds. For enhanced security we recommend enabling HSTS as described in our security tips.

Except, they all are! And if I connect to the container via docker exec -it owncloud-server bash I can ping / curl to my heart’s content.

Everything works fine - I can login, access files, sync with desktop, the apps work fine, so I think it’s not a problem with the setup but with the warnings?

The annoying thing is that I can’t connect to the marketplace to update / install apps any more - despite the fact I have previously, and definitely under 10.6.

Is it safe to downgrade to 10.6 to check if I get the same warnings, now I’ve upgraded to 10.7?

Is there anything else I can do to test the config? As I say, I’ve had this config working since a fresh install under 10.4.

OK so apparently owncloud is setting the headers, as is my proxy server, so they are appearing twice - is there any way to stop owncloud doing this?

That solves the header issue - but the no internet connection issue is very strange - especially as I can connect via docker exec and can quite happily connect to the outside world.