So this is probably two problems linked to the same problem. Today, me and two friends tried playing together on multiplayer. One of them could see the multi salas perfectly, me and the other one could not, we could only see each other and either one or two games or none at all (gyazo shows no rooms). Same as before. It only started from today onwards, so it might be related to a recent patch dev have put on.
On the second part, we tried adding each other via Xbox Social and then Invite, but it led to an error.
That confirms you are not running on the latest version, which is 18493 rather than 14825.
Unfortunately, the Store is very buggy when it comes to updates. You might need to reinstall the game or something, I’m not sure how to force an update. On Steam this works perfectly; game is always updated before/upon launch so it’s not possible to have wrong version.