Lightbox not showing up on uploaded images after update

Installation
9

Thanks for the suggestion. Safe-mode did not work out, Lightbox is still not working.

We indeed have a outer nginx-proxy that is forwarding HTTPS-traffic to the nginx located within the discourse-container (also configured for https). Could that be an issue? If yes, what could be the deal?

server {
    listen 443 ssl http2;
    server_name ###mydomain####;

    client_header_timeout 5;
    #client_body_timeout 15;
    client_max_body_size 300m;

    include /opt/nginx/conf/ssl.params;

    proxy_http_version 1.1;
    #proxy_connect_timeout 20;
    proxy_read_timeout 360;
    proxy_pass_header Date;
    proxy_pass_header Server;
    proxy_pass_header Authorization;
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For  $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto https;
    proxy_pass_request_headers on;
    proxy_set_header Accept-Encoding "";
    proxy_buffering off;
    proxy_set_header Connection "Keep-Alive";

    location / {
            proxy_pass https://##internalip###;
            proxy_redirect off;
    }
}