Originally Posted by: Mechberg 
[UPDATE: 10/3/14 5:25 p.m.]Finally, we have seen some complaints from players who are unable to connect to multiplayer services in Forza Horizon 2. We are investigating this issue within Forza Horizon 2 but I also want to remind players about issues regarding NAT errors on Xbox One. If you are unsure of how your home network is set up, or the state of your NAT settings,
this is a good support article found over at the Xbox Support site to help you troubleshoot. Those of you who are still having issues with multiplayer should let us know in this thread so we can follow up.
That would be me. Have been trying since the mid-night launch with no luck. It finds the match, i join it, i'm in for anywhere ranging from 1 second to 45 seconds, then i'm dropped. I can see the player list load in, i can hear everyone chatting, i can get a nav point for the nearest event, ect. In every indication, I am in the game. But without fail, I will lose connection.
I read the support article you linked, NAT is open, couldn't find a IPsec setting in my belkin set-up page, but i did Disable/Enable UPnP, restarted router, hard rebooted console, ran network diagnostics and by all indications, I should be good to go.
I can chat, join parties and play MP in every title i've owned so far on XB1. But this has been a very disappointing experience. I don't care about the rewards and whatnot, i just want to play an online road trip. =/