You’ve lost the internet connection to Zwift’s servers. As long as you get that back for when you’re saving, it will save ok. So don’t save it until you see the other riders come back again.
You may still be able to get your ride information and upload it to a third party site like Strava or Garmin.
This Support article has steps for recovering the .fit file from your ride if you need it. once you have that you can manually upload it so that you still have a record of it and can view your breakdown.
If you have any issues with it, please let us know.