I’ve got the same problem, I’ve touched all ports parameters, from nginx on web server and nginx on opnsense waf. Finally I’ve VLANed the webserver and added a vlan on lan interface of opnsense then I configured to use plain HTTP 80 port on webserver. And assigned 80 ports on the upstreams on nginx in opnsense. That’s the fastest way I found to solve that problem with WordPress. Vlanning also increases a little bit your security anyway.
