The only thing that seems to work to fix this permantanlty is to delete Roons cache folder. Locate the folder for your specific operating system. Stop Roon then delete the contents of the cache folder or you can rename the folder if you want to instead, this is located in the Roon Server directory. Restart Roon all should be fine. I have given this advise to most users having this issue and it works. A reboot might clear it to but it often returns after some time.