Wireguard works only after firewall rules reload

[hypersonic]

Hi,

I installed an OPNsense in our Proxmox Enviroment as a VPN Gateway with Wireguard. The reason for this setup is having a gateway with a static IP Address to reach our management interfaces from a defined IP Address.
So the OPNSense has only one (1) "physical" interface, the WAN Interface with a static ip.
I followed the WireGuard RoadWarrior Setup including Set 4a, with a extra WireGuard Interface: https://docs.opnsense.org/manual/how-tos/wireguard-client.html and everything works fine, but not after a reboot.

After a reboot, connecting a client, traffice will not pass through the tunnel.
To solve this issue, I have to go to Firewall-Rules-[WireGuard-Interface], press Edit, Save and Apply (without any change). Now the traffic passes the tunnel.

And I tried already 2 things:

a) I downloaded the configuration after a reboot and after applying no-changes to the firewall rules. Both files are exactly the same
b) I also did a complete re-install - with the same result.

Does anyone have an idea what could be the cause of this issue?

thanks, rainer