Cannot reach (ping) HomeAssistant from Gateway only


I have a weird situation, am running HA Supervised in the following version:

Version	core-2022.6.7
Installationstyp	Home Assistant OS
Entwicklung	false
Supervisor	true
Docker	true
Benutzer	root
Virtuelle Umgebung	false
Python-Version	3.9.12
Betriebssystemfamilie	Linux
Betriebssystem-Version	5.15.45
CPU-Architektur	x86_64
Zeitzone	Europe/Berlin

Host-Betriebssystem	Home Assistant OS 8.2
Update-Channel	stable
Supervisor-Version	supervisor-2022.05.3
Agent-Version	1.2.1
Docker-Version	20.10.14

I am troubleshooting why I cannot reverse proxy my HA htough opnsense. The reverse proxy works in general, when I am replacing the upstream server with another one I can access it from outside.
But the Homassistant server cannot be reached. I can ping every other device on my network from OPNSense, but when I ping (homeassistant ip, double checked) from my opnsense the ping times out. When I ping homeassistant from any other machine, it responds.

I am not aware of anys firewall settings I made on the HA machine, I don’t even know if there is anything like this.

I played around with the configuration.yaml, currently it looks like this:

  #internal_url: "http://homeassistant.local:8123"
  #base_url: https://homeassistant.local

  use_x_forwarded_for: true
  #base_url: ""

What can I do?