How did you do the reverse proxy? I created a sites-enabled and sites-available folder under etc/httpd and made a drupal.domain.com file with all the code I needed for reverse proxy, I can post it if you like. Then make a symlink to sites enabled and restart apache and youre done. Oh, you need to make sure apache conf file is looking for your conf files in sites-enabled but that should be there by default. Thats how I do all of my reverse proxy stuff, I have several sites I run, some on the gateway and some on another server and that works fine. You need to set up letsencrypt for the new drupal though, so that the reverse proxy will use the letsencrypt cert.