@Viktor Jaep glad to hear your OCD is healthy and happy - I think you know we share a common bond there!
Based on some extra emails I'm getting from wan-failover (since re-installing vpnmon-r3) on a reboot, where it senses WAN0 is disconnected and then reconnects shortly after, I think there may be some kind of "tussle" going on but it's maybe a startup timing issue between the two scripts?
I might try playing with the respective delays of starting up VPNMON-R3 and WAN-FAILOVER and see if I can make it play nice, or do you have any other thoughts?
Your script doesn't restart the WAN interface does it? Trying to work out which should "settle" first ...
I have your "Provide additional WAN/Dual WAN monitoring" option enabled but what exactly does that do? Could that be playing into it?
Cheers and hope you are well!
StephenH