My son and I had an issue with Infinity 2.0 that still exists with 3.0. If either of us tries to invite the other to a game, the invitee accepts the invitation, goes to a load screen, then the spinner freezes around the Infinity logo and the invitee is dropped to the Xbox One dashboard. The same thing happens if either of us tries to join a game in Flynn's arcade.
I've done about every troubleshooting thing imaginable. Our NATs are both "open" and I even went so far as to purchase a block of static IP addresses from AT&T to see if that would work. We have no issues with any of our other games.
I'm to the point that I think there is something specific in the Infinity multiplayer code that conflicts with the Motorola NVG589 cable modem / router combo that AT&T U-Verse uses. I've also read posts from a couple Comcast users who have experienced similar issues.
I'm curious as to if anyone either has experienced this (and if so, who is your ISP and what is your router)? And if you use U-Verse and the NVG589 and online multiplayer IS WORKING, I'd love to compare router configs with you.