Scheduled to begin today and run through to next week's launch the open beta for Rainbow Six Siege across all platforms (PC, Xbox One, PS4) has been delayed due to matchmaking issues. But on the bright side it looks like the issue is being resolved, so it should only be a matter of hours before you can test out the new Rainbow Six.
According to a post on the official forum
, "Game sessions are not starting properly and we’ve encountered server issues, leading to failed connections. We’ve identified the root issue that was introduced after the Technical Test while fixing a separate aspect of the game. A fix is currently under test and will be deployed within the next few hours. Within the next few hours, we anticipate pushing the fix initially to Xbox One and then PC and PS4 as quickly as possible thereafter."
With the game launching on December 1, it's probably safe to say that this beta is more of a test run for the full roll-out. And having these sort of issues now is a lot better than running into day one matchmaking problems.