This issue should be resolved as of the 9/29 update. The game will repeatedly retry to send you to the event start if the first attempt fails.
After a user registers for an event, they should be presented with a prompt to go to the event waiting area up to 30 minutes before the event starts and see a Join Event button in the lower-left corner of the screen. We've seen cases where the user isn't teleported after they click either of these buttons or lets the prompt time out without dismissing it, however.
If you're sure that you've registered for an event correctly as outlined in our knowledge base article, but either haven't seen the prompt to join the waiting area <30 minutes before the event starts, clicking the prompt doesn't teleport you, or you aren't teleported at the end of the prompt, log out and back in to the game, then click the Join Event button in the lower-left.