Ho, okay, my probleme come from the checkbox.
Since I don't have a valid certificate for the moment, it was the webConfigurator default certificate which was used, hence the "pfsense-5e2183c31ebed" host verification.
It's weird because I don't remember unchecking this option, but if I create a Frontend in my Haproxy 59_20, it's indeed checked by default. I must have a bad memory.
Thanks PiBa =)