conclusion
I got this problem as well. and now I’ve solved it.
solution
I’ve modified the /etc/gitlab/gitlab.rb file, changed into
nginx[‘redirect_http_to_https_port’] = 80
nginx[‘listen_port’] = 443
and sudo gitlab-ctl reconfigure + sudo gitlab-ctl restart, and it works.
process
in the past, the reason i could connect to gitlab server is because that my colleague have set something in the /var/opt/gitlab/nginx/conf/gitlab-http.conf file.

Redirects all HTTP traffic to the HTTPS host
server {
  listen *:80;

  server_name gitlab.xxxxx.com;
  server_tokens off; ## Don't show the nginx version number, a security best practice


  location/{
    return 301 https://gitlab.xxxxxx.com:443$request_uri;
  }

  # health checks configuration
  include /var/opt/gitlab/nginx/conf/gitlab-health.conf;

  access_log  /var/log/gitlab/nginx/gitlab_access.log gitlab_access;
  error_log   /var/log/gitlab/nginx/gitlab_error.log;
}

server {
  listen *:443 ssl http2;


  server_name gitlab.xxxxxx.com;
  server_tokens off; ## Don't show the nginx version number, a security best practice

and once if I’ve use the command sudo gitlab-ctl reconfigure, and the file gitlab-http.conf would be covered by /etc/gitlab/gitlab.rb. and the nginx settings in /etc/gitlab/gitlab.rb would start to take position that makes me cannot visit gitlab server after using the command sudo gitlab-ctl reconfigure. and now I’ve set the nginx settings right in /etc/gitlab/gitlab.rb just like in the solution part. hope it could help. thx.