OPNSense Web GUI partially empty when accessing through haproxy

[psyko_chewbacca]

Hi,

I have a reverse proxy setup to access OPNSense own Web GUI through it.
When accessing directly with IP of OAN interface, all is fine.
When accessing through haproxy via the domain (all setup with letsencrypt), some of the menus are not populated with settings. I noticed it happens mostly for settings pages related to services.

haproxy is setup to listen on 0.0.0.0:443 and OPNSense Web GUI is set to listen on port 80.
I have setup a very basic reverse proxy, no SSL pass through, backend server is set to the LAN interface IP. Same type of config works just fine for Adguard plugin bound to port 3000.

Any ideas why some menus are not populated when accessing through haproxy?

Thanks.