MULTI-WAN link showing 'DOWN'

Yes, I executed this command. Indicates that there is a connection. But switching does not occur.

There is a problem. Multi WAN is configured by red1 and red2.
Red1 static ip channel 100 megabits (weight indicated 100)
red2 is a backup channel adsl, 15 megabits (weight indicated 50)

Constantly switching to red2, no return to red1.
If you disable red2, then the Internet through red1 works stably.

We had some issues with some routers. As I said you need to debug icmp through red1 with tcpdump when red1 is down.
We need to see tcpdump output as a copy and paste.
In our case, the workaround has been to change ping interval to 35 seconds.