"Unable to join session."

How many times have you gotten this in a row?

Today, I was able to get this message 13 times before I was successfully able to join a lobby =P

if you’re getting it while searching for ranked it just means someone got in there before you. if you’re getting it in endless it’s either full but there’s also some sorta glitch where people can’t enter eachother’s endless lobbies. on top of the endless lobby slowdown glitch.

“Endless Slowdown Glitch” ? Never heard of this, what is it?

That’s not a glitch, people just need to open their ports. Everyone so far who’s been unable to join me had a “Moderate” NAT under Home > Settings > Network information on GFWL.