Last 2 rides I’ve noticed I seem to be the only rider! The first was a workout in Watopia that saved fine, but today I was in Richmond with lots of other riders, and 10mins from end of workout everyone disappeared! Then, my activity didn’t save properly - I can see it in the companion app, but cannot load the details and it hasn’t synced to Strava. I’m using a Tacx Bushido Smart trainer, and my device has an internet connection, so not sure if this is down to a bug in a recent update? Have been using it without any issues for the last few months. The app is v53029-1.0.53028.
The symptoms you describe are consistent with connectivity issues. These result in no other riders shown, and corrupt/incomplete ride upload to Zwift (and, by extension, Strava).
You might want to try https://zwiftalizer.com/ for more info.