Please open the Style Picker and click the Rebuild button; you can do a Fast rebuild. Then go to Help | What add-ons do I have. Look specifically at the RealTracks Sets and RealDrums Sets Not Found sections, and see if there are any Sets are listed there. If there are RealTracks or RealDrums Not Found, please re-install the Sets numbers listed.
If you are using Mac you would manually install the RealTracks. This video goes over how to download and install RealTracks for Mac:
https://youtu.be/pF8ozIFmOe4 If you are using Windows, you can either manually install the RealTracks or use the Download Manager.
Here is our video on downloading and installing RealTracks manually for Windows:
https://youtu.be/vHfatrraj_k Info on how to use the Download Manager is here:
https://www.pgmusic.com/tutorial_downloadmanager.htm