Hi Maxim,

thanks for your help - I really appreciate it!

I have this line in my cfg:
error_page 497 https://$host:8080$request_uri;

As I said I'm using ispconfig, and this is part of its configuration for the ispconfig web admin interface. See https://git.ispconfig.org/ispconfig/ispconfig3/-/blob/develop/install/tpl/nginx_ispconfig.vhost.master

So, you're saying the 497 redirect is the problem. I.e. removing the error_page directive or returning a static error page would solve the problem? I will try as temporary workaround.

Apart from this quick solution, I probably need to file a bug report for Debian. I don't want to manually update a single package but rely on the packages in Debian's stable branch.

Thanks,
Daniel