Rainbow Six: Siege was supposed to transition from closed beta into an open beta phase later today, but that's no longer happening.
In a post on the Ubisoft website, one of the company's community managers has explained that earlier plans to transition Rainbow Six: Siege into an open beta have been temporarily shelved, due to failed connections on all platforms.
"Game sessions are not starting properly and we’ve encountered server issues, leading to failed connections," Ubisoft posted. "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."
All platforms are affected and an update has been pushed out. Ubisoft says they are "monitoring how the fixes impact the game experience throughout the night" and that the game will remain in closed beta until further notice. "We will give you another update tomorrow at [10:00 AM] EST," Ubi said.