DNS over tls when running two different servers

[DEC740airp414user]

I subscribe to nextdns and controld

I've been using controld as my only dns over tls server.   Well today their service was down for about an hour.     It had been a Long time since I enabled two servers.  Today  I enabled both services I subscribed too.

I then logged into the nextdns website, and every sec it said I was using their service then it kept going to red saying I was not


Can anyone explain how dns over tls works when you have two servers added?