Still happening today. A little more info though, yesterday I was able to play a bunch and only had it happen a few times. Today all day I've been attempting to play, and it's only let me join once or twice. Meaning mostly working fine yesterday, and mostly not working fine today.
I too am also experiencing this again. All day today I've been trying to play, and it's let me one or two times out of 10 attempts or more at joining.
Update, I switched to a different profile on my Xbox and it let me log into multiplayer with that account. When I switched back to my other Xbox account it gave me the same error as before and won't let me connect. I switched back to my other Xbox account and then it again didn't let me join.