Happened twice now over the last week, join Countdown and end up in a raid, link to video, as you can see it has a countdown timer and info on the bottom left about countdown but yet we have been transferred to a raid.
If you cannot see the video via the link than tell me, i will upload it to you tube instead (link works for me):
https://gamerdvr.com/gamer/oatiecrumble/video/166438330
Heya @Oatiecrumble!
If you haven't already then please try out these steps, and then if the issue persists, please upload your video to YouTube so that I can send up a bug report! 
@Oatiecrumble Thanks!
I'll get started on typing this up, but would you mind getting us a video that begins with you selecting the option to matchmake for Countdown? I also saw that the exit button at the end of your video said exit Countdown, so please include that in the video as well!
Hello @Oatiecrumble,
I totally understand that the issue appears randomly.
In order to forward this to the development team, we need to be able to replicate the issue, so they can have a look into this themselves.
I will document this report to keep track of this issue.
Thank you for reporting such a behaviour.
devtrackers.gg