@stefan-bendler
If you go to the settings page in HAproxy you can find a button at the bottom to display the whole configuration and would also give information about your backend settings.
From the given information it's not clear to me, what you intend to achieve and what's not working.
I'm wondering, if you're using a public IP inside your network.
If this is your public external IP you may want to hide it.
From your screenshots, I assume the http is working as expected, but for the https obviously gives you the pfSense web GUI.
Is the web configurator listening on the same port as the HAproxy frontend? If so you can change it in System > Advanced > Administration.