Started the B / Standard ride for TDZ stage 2 and around the second half, it seems to have dropped me out of the group event and am now riding solo like a standard select a route / freestyle ride. Never had this happen before… anyone else?
Riders disappearing is due to the network between you and Zwift disappearing and not recovering soon enough. A router/modem reboot can sometimes fix this, it can also be a local issue like wifi interference, or even your ISP having bit of a glitch. If its a one-off, probably not a lot you can do (still do a modem reboot anyway) but if it becomes persistent, its fairly easy to troubleshoot/isolate.
You can also throw your log file onto zwiftalizer.com which will likely provide a few more details around the issue you had.