Authelia with Nginx on latest

So recently I updated from the :v2 tag to :latest and my Authelia setup just broke.
Until that, I could just not enable the built-in auth, got redirected to Authelia, then after successful authentication directed back to SB.
Now on the last step I get “400 Bad Request”
The same Authelia setup works for every other app I host.

    - domain: my.domain.com
      resources:
        - '/\.client/manifest\.json$'
        - '/\.client/[a-zA-Z0-9_-]+\.png$'
        - '/service_worker\.js$'
      policy: bypass
    - domain: domain.com
      policy: two_factor

I use nginx as reverse proxy (not nginx proxy manager, I do it raw) with the following settings:

server {
    server_name my.domain.com;
    listen 80;
    return 301 https://$server_name$request_uri;
}

server {
    server_name my.domain.com;
    listen 443 ssl;
    listen [::]:443 ssl;
    http2 on;
    resolver 127.0.0.11 valid=10s;
    resolver_timeout 5s;
    
    include authelia.conf;

    ssl_certificate /etc/letsencrypt/live/domain.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/domain.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot  

    location / {
        proxy_set_header Host $http_host;
        set $upstream_silverbullet silverbullet;  
        proxy_pass http://$upstream_silverbullet:3000;
        include auth.conf;
        include proxy.conf;
    }
}

where the included configs are based on NGINX | Integration | Authelia
But thats a lot. I cannot figure out which one is incorrect.
In the nginx logs I can see the 400 response code, but no error at all.
SB logs show nothing.
I’m stucked, dont know how to proceed.
Does anyone have a working example with SB + Nginx + Authelia care to share so I can compare whats wrong with mine?

The :v2 is the latest main (edge) build which has some fixes for authentication proxies like Authelia, :latest is from a few weeks ago and doesn’t yet have those fixes. Are you sure you want to downgrade if your previous setup worked?

Actually my “upgrade” was couple weeks ago when the new Share feature was released that I wanted to try out. I assumed the :latest contains that. Authelia broke that time, I just did not had the time to take care of it until now.

Upon the suggestion, I switched back to :v2 now, but no change, I still get ‘400 bad request’ without any error in the logs of SB/Nginx/Authelia.
Not sure how to debug any further.