@oki:
in your current haproxy setup (initial post), you do ssl offloading and do ssl encryption again on your backend.
1. is your backend webserver listening on port https://10.10.10.52:443 and can you access the webserver using https?)
2. when reencryption is not needed in your LAN, switch "SSL off" for your backend. and change the HAProxy Backend to your http listening port. (maybe http://10.10.10.52:80 ?)
3. Verify, that the status for your backend is Up in haproxy.
4. if 1 to 3 is successful done, verify that you are using the correct Certificate for your Frontend. (DO NOT USE the pfsense WebUI Certificate, neither a (root) CA certificate). It's needed to use a SSL-Webserver certificate, as issued from Let's encrypt.
It work like a charm when I switch SSL off on my backend and change my http listening to 80 !
I also put the verification method back on HTTP.
I'm doing more extensive functional tests tonight and I'm making a return to you and DRago_Angel!