I'm going to try and do a better job explaining my issue.
I have a multi-WAN setup. I also have a group gateway setup for failover. I have devices connected to my LAN. One of those devices is another router.
Here is my problem: If I select any other gateway other than "default" in the firewall the other router stops working but the rest of my LAN devices works correctly.
I have tried many combinations of settings and am still stuck. I have unchecked the "block private networks" on each of my WAN interfaces.
What am I missing?
Missing outbound NAT is my guess