Why do I get the one or more players not ready when we ARE ALL READY?
This was happening to me for a while too.
I figure out that if you add everyone that’s in your party to your friends list, then it would work most of the time. We were going in with 4’s no problem for like 5-6 games straight.
We did it 5 times. Didn’t work. 1 hour later and everyone quit. 
Glad it worked for you though.