There is clearly a Zwift bug unrelated to network connection issues that results in riders seemingly randomly disappearing and reappearing in events, but I’m not sure this has been acknowledged by Zwift anywhere yet.
An example I posted into the January update thread earlier: in Tuesday’s ZRL TTT, one of my teammates couldn’t see anybody else for maybe 15–20 seconds but the rest of us could fortunately still see her pulling the group (and hear her on Discord as well).