I signed up for 2 rides today on the mobile link. On each occasion the timer counted down to the start time( in mobile link on iPad), but in Zwift (on computer) I was given not the option to join the ride.
All other functions seemed to be working correctly.
Had you started pedalling in Zwift? For me the join button pops up after I start pedalling. I usally do a warmup then let it auto join me when the timer gets to 4 min 30 seconds.
I was already on a ride and wanted to join a DDQ ride. I have not previously experianced problems being ported to start gate for an event.
This seems to have be a temporary hiccup. I signed up for an event yesterday and was teleported in the normal manner. All is well 
I had the same problem today, and it has happened before. I signed up for a ride, and was not teleported to the start. I tried a couple more rides to see what happened. Still no luck.
I’m operating on the iPad app.