How is your RUTX11 setup as the WAN failover device for your primary network?
I have mine setup as the WAN2 failover device for my Unifi UDM Pro main WAN1 network. When that network is down, after ~30 seconds (not configurable that I can find), then UDM flips to WAN2, and routes all traffic to my RUTX11, which then kicks in and does SIM1 => SIM2 switching/failover or load balancing, depending on how I've configured it.
When my WAN1 comes back up, UDMP automatically fails the WAN2 => WAN1 back over, and traffic then flows over WAN1 as the primary WAN interface.
What does your network topology look like?