So.. This looks to be a fairly similar issue to this one https://github.com/opnsense/core/issues/2841.Could you try this as mentioned by AdShellevis:"Can anyone with the issue try to disable "Automatic outbound NAT for Reflection" in Firewall->Advanced and test again? As far as I can see that's these are the only areas in the code generating a rule with as target an interface."
In that case, it might be worth applying the fix also mentioned in that thread.Down the bottom there's a fix that should apply for 20.1.7