Something that I didn’t see mentioned here is privacy settings. If your xbox account is set to block your online status you may show up as disconnected in game even though in the xbox companion app you show as online. This change along with making sure that the xbox networking services where running allowed me to group and fly with some friends. I’ve still had intermittent issues though with the multiplayer so there could definitely be some other bugs that need to be worked out.
You can change it by following these instructions: Xbox Support
On the Privacy tab, make sure that you have set “Other can see if you’re online” to either everyone or friends.
