Here is mine https://gist.github.com/jeena/6179470a8d616455f30635a5c71f5f64 which had a similar problem with the comments, although I couldn’t post comments on my own instance either.

For me the thing was that I had to add:

map $http_upgrade $connection_upgrade {
    default upgrade;
    ''      close;
}

and

        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection $connection_upgrade;

And also change the nginx in the docker to port 8080 so my normal nginx could keep running on 80 and handle all the ssl certificate stuff.

My setup is:

Browser -> native Nginx -> docker Nginx -> lemmy