Other riders disappearing and reappearing

In my last ride, other riders kept disappearing and reappearing very frequently - probably every 2-3 minutes. No clue why - but quite annoying.

I have never had a ride where this doesn’t happen.  Many have suggested a problematic internet connection, but www.pingtest.net shows that I have a 21ms ping to Lynnwood, Washington, with 0% packet loss and 0ms jitter.  I consistently get >24Mbit/sec from www.speedtest.net.  It’s hard to imagine that Zwift requires a better connection than that.

Even more annoying is the complete lack of any response from Zwift support after filing a trouble ticket over a week ago.