Issue with HA Proxy 3.8

[rupesh4321]

HA proxy isnt working for few backends. I have no error in haproxy connfiguration setup that is for sure. My scenrio is like this.
 
=> http real server  10.10.10.xx(xampp apache)
=>https real server 10.10.10.xx(nextcloud)  [this is https with valid certificate at server itself as well]
=>https real server 10.10.10.xx(mattermost)  -[this is https with valid certificate at server itself as well]
mand many more like this

backend are configured for each server

front end listens on 0.0.0.0:443 with valid certificates issued via acme client on opnsense

issue - everything works as expected except that mattermost webserver. if i disable haproxy and try to access mattermost using NAT. It works as the client also has ssl certificate installed, and then if i revert back to nat disable/haproxy enable then also its working. But as soon as i restart my firewall mattermost stops working.

why is this happening with me. i can assure thatt there is no error i can find in configuration. infact mattermost is accessible form internal network without any issues. This was working with opnsense earlier.

Please help me on this. If any logs are needed then pls feel free to mention/ask.. just get this setup working