Gateway Groups - Incoming traffic being responded to on wrong IF

[Alphakilo]

Hey fellow OPNsense users!

I've set up multi WAN as a failover group as described here: https://docs.opnsense.org/manual/how-tos/multiwan.html

Attached is a screenshot of the gateway groups.

The interfaces are pppoe0 and igb3, for WAN and Vodafone respectively. I have some services running on pppoe0 (namely OpenVPN and NGINX) locally, which both broke after the upgrade. Turns out, OPNsense is answering to incoming traffic on pppoe0 via the wrong interface, igb3. I can't really make sense of it ???