Do you have two default routes in the routing-table when both are up? Then you might want to stop its injection by both circuits (set defaultgw disable) and put two static default-routes in with different distances to have only the main default-route toward wan1 is in the routing table when wan1 is up.
I do have 2 default routes:
dest: 0.0.0.0 gw: <wan1-gw> distance: 10 Priority: 0
dest: 0.0.0.0 gw: <wan2-gw> distance: 10 priority: 10
I am not sure the routes are the issue? when wan1 comes back online, all data properly reverts back through that connection... but bc the VOIP connections basically always stay on, the only way to get them to fail back to wan1 is to literally unplug or disable wan2.
What can I add to my config to forcibly drop those VOIP connections when wan1 comes back online? ( and yes, i know it would drop any existing calls )