SOLVED: Severe stuttering via reverse proxy (nginx)

Code:
server {



    server_name jellyfin.mydomain.com;



    ## The default `client_max_body_size` is 1M, this might not be enough for some posters, etc.

    client_max_body_size 20M;



    # use a variable to store the upstream proxy

    set $jellyfin 192.168.7.8;



    # Security / XSS Mitigation Headers

    add_header X-Content-Type-Options "nosniff";



    # Permissions policy. May cause issues with some clients

    add_header Permissions-Policy "accelerometer=(), ambient-light-sensor=(), battery=(), bluetooth=(), camera=(), clipboard-read=(), display-capture=(), document-domain=(), encrypted-media=(), gamepad=(), geolocation=(), gyroscope=(), hid=(), i>



    # Content Security Policy

    # See: https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP

    # Enforces https content and restricts JS/CSS to origin

    # External Javascript (such as cast_sender.js for Chromecast) must be whitelisted.

    add_header Content-Security-Policy "default-src https: data: blob: ; img-src 'self' https://* ; style-src 'self' 'unsafe-inline'; script-src 'self' 'unsafe-inline' https://www.gstatic.com https://www.youtube.com blob:; worker-src 'self' blob>



    location / {

        # Proxy main Jellyfin traffic

        proxy_pass http://$jellyfin:8096;

        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-Protocol $scheme;

        proxy_set_header X-Forwarded-Host $http_host;



        # Disable buffering when the nginx proxy gets very resource heavy upon streaming

        proxy_buffering off;

    }



    location /socket {

        # Proxy Jellyfin Websockets traffic

        proxy_pass http://$jellyfin:8096;

        proxy_http_version 1.1;

        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-Protocol $scheme;

        proxy_set_header X-Forwarded-Host $http_host;

    }



    access_log /var/log/nginx/jellyfin.mydomain.com-access.log;

    error_log /var/log/nginx/jellyfin.mydomain.com-error.log info;



    listen 443 ssl; # managed by Certbot

    ssl_certificate /etc/letsencrypt/live/jellyfin.mydomain.com/fullchain.pem; # managed by Certbot

    ssl_certificate_key /etc/letsencrypt/live/jellyfin.mydomain.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 = jellyfin.mydomain.com) {

        return 301 https://$host$request_uri;

    } # managed by Certbot



    listen 80 http2;



    server_name jellyfin.mydomain.com;

    return 404; # managed by Certbot



}