Symfony Panther shows errors in chrome console err_tunnel_connection_failed when using proxy server

Question

Scraping using Symfony Panther works fine, but when I preform the same scrape using a proxy, the requested website will not load resources. I get errors in my google chrome console "err_tunnel_connection_failed"

Here is my Client set up

$args = [
        '--user-agent=Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36',
        '--window-size=1600,1100',
        '--no-sandbox',
        '--proxy-server=http://' . config('services.panther.proxy_host') . ':' . config('services.panther.proxy_port')
    ];

    // create a chrome client
    return Client::createChromeClient(base_path('drivers/chromedriver'), $args, []);

If I remove the --proxy-server=... everything works fine.

Any ideas what is going on here and how to fix?