Ubisoft had to delay the scheduled open beta for Rainbow Six Siege which should have started today due to issues on the PC, Xbox One and Playstation 4.
According to an update on Ubisoft's forum, there are certain issues with matchmaking times and disconnection problems on all platforms, forcing Ubisoft to delay the open beta phase and still keep the game in closed beta status until those issues are resolved.
In case you missed it, the open beta was announced earlier and it was quite strange that Ubisoft decided to hold an open beta phase so close to the offical launch date, scheduled for December 1st. The open beta phase should include three maps and three game modes.
The open beta phase has been postponed to a "later time" and it appears that Ubisoft won't change the original December 1st launch date.
Source:
Ubisoft forum.