Only page title gets loaded - node.js

Question

I'm trying to set up a Debian 11 server with wikijs. As a webserver I use Nginx with a Let's Encrypt ssl certificate. The ssl certificate was created using certbot.
The site should be available under it's internal ip at port 7443 as well as https://wiki.url.com:7443
Wikijs config.yml:
port: 3000
db:
type: postgres
host: localhost
port: 5432
user: someuser
pass: somepassword
db: somedb
ssl: false
sslOptions:
auto: true
schema: public
ssl:
enabled: true
port: 7443
provider: custom
format: pem
key: /etc/letsencrypt/live/wiki.url.com/privkey.pem
cert: /etc/letsencrypt/live/wiki.url.com/fullchain.pem
passphrase: null
dhparam: /etc/letsencrypt/ssl-dhparams.pem
Node.js config file:
server {
server_name wiki.url.com;
# security
# security headers
add_header X-XSS-Protection "1; mode=block" always;
add_header X-Content-Type-Options "nosniff" always;
add_header Referrer-Policy "no-referrer-when-downgrade" always;
add_header Content-Security-Policy "default-src 'self' http: https: ws: wss: data: blob: 'unsafe-inline'; frame-ancestors 'self';" always;
add_header Permissions-Policy "interest-cohort=()" always;
add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;
# . files
location ~ /\.(?!well-known) {
deny all;
}
# reverse proxy
location / {
proxy_pass http://127.0.0.1:3000;
proxy_http_version 1.1;
proxy_cache_bypass $http_upgrade;
# Proxy headers
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
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 $scheme;
proxy_set_header X-Forwarded-Host $host;
proxy_set_header X-Forwarded-Port $server_port;
}
listen [::]:443 ssl ipv6only=on; # managed by Certbot
listen 443 ssl; # managed by Certbot
ssl_certificate /etc/letsencrypt/live/wiki.url.com/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/wiki.url.com/privkey.pem; # managed by Certbot
#include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
}
server {
if ($host = wiki.url.com) {
return 301 https://$host$request_uri;
} # managed by Certbot
listen 80;
listen [::]:80;
server_name wiki.url.com;
return 404; # managed by Certbot
The weird thing is that it has worked before on port 80 without any problems, until we installed the certificate using certbot. This tutorial was used after multiple failed attempts: https://www.vultr.com/docs/how-to-install-wiki-js-on-debian-11