I signed up for an event, my first, and got a notice to join the event but when joined there were no other riders and then ride started and it was only me. So I stopped and changed courses as ride was on a course not open today so no other riders. But when I went to the other course all the messages in the Zwift App were for the ride I had tried to join so showed other riders. Not sure what I did incorrectly as did what I did last year for Tour de Zwift and it worked fine.
Sounds like a network dropout. Did your connection get interrupted during the ride? I believe you can enter the file at www.zwiftalizer.com to find out if you lost connection.
No when I joined it put me at the line with the clock counting down my avatar on a trainer. Just no one else there and there were a lot signed up.
I’ve had that happen too. I just rode the event, and within a couple minutes, the rest of the group suddenly appeared all around me. It was a little weird though, while I was riding all alone