Sorry that you are having some issues. Did you try updating the Galaxy Wearables App? Once you do this please reconnect the Gear S3 with the S20+ in the app. If updated and still does not work, see if your setting was changed in the apps and watch settings. The tracker may have been turned off. I hope these troubleshooting solutions have helped you.
I do hope I have helped you to the best of my ability. If you have any further questions I would love to be your trusted advisor. Have a great day and thank you for choosing Samsung.