Ubisoft is known for not having good servers, but I have never had a problem with the servers on Rainbow Six since the game came out. Ever since White Noise came out my friends and I have been lagging out of matches frequently, then we join back and will get an abandonment sanction for something that we didn't do. It de-ranks us every time too. I know other players are experiencing the same thing. Please fix this, I love the game.
Without more information I can't really give you any good advice, so my suggestion would be to send in a ticket to support and go through the troubleshooting process. That way we can start to try and diagnose the problem before we look for a solution.