Hi... Finally I got some time and window to get back.
Just tested the 2.1.0 version which seems near to fulfill the wan-failover purpose, but is not there yet in my case.
I removed any traces from the previous installation and rebooted the router before install the 2.1.0 installation and rebooted again after (I did no changes to wan-failover config).
The router came up with WAN0 as the primary and I let it ran for almost 15-20 minutes before switching OFF the ISP router providing the service to WAN0.
At this point the WAN1 took the primary role and again I checked that it remained stable for 15-20 minutes.
Then I switched ON the ISP router providing the service to WAN0 but WAN1 kept the primary role.
After that I entered the wan-failover menu and forced the failover to WAN0, but it didn't work either.
During all the testing process, I noticed high CPU usage not only during the phases where the services were being restarted, but always which makes the router performance not good.
View attachment 53908
So I had to remove the script and restart the router again.
View attachment 53907
Thanks for you work and support but I guess it's time to invest in a new non Asus router.