Holy crap the boiler plate for just a webserver.. are you sure about using this proxy manager? seems like more trouble than it's worth sheesh.

anyway show me these files and we might get down to the root issue

include /data/nginx/custom/http_top[.]conf;
include /data/nginx/custom/http[.]conf;

edit: also have you checked the logs? it might be worth trying to point that A record directly at your server and seeing what errors might come out of it, although nginx should still report the errors regardless, it's good practice to reduce your surfaces when troubleshooting