MWan3 adding a route /1

Hello,
Since I installed mwan3 on OpenWRT, sometimes, which I did not discover what triggers it, a route of default/1 is added and then all traffic outside gets broken and internet access is lost!
I have to manualy putty into the router and "route del" that route to get internet access back!
What triggers this route to be added and how to prevent it?
Thanks.