Music library disappeared - not using sync library
Running macOS 10.15.1 on a 2017 5k iMac. Upgraded to Catalina a couple of weeks ago. Music (app) has worked fine for me until now, although I did lose some covers in the upgrade.
I do not use Apple Music (the service) and have not turned sync library on as I do not have enough iCloud space.
I have an iTunes library of approx 1TB stored on an external SSD. I use an alias to point the Music folder to this location. Within the Music folder my library is still in an iTunes folder. There is also a new Music folder, which has three items in it that I have recently added.
Today I noticed that my Music (the app) library was almost empty as I added some new files to it. I think I last synced to my iPhone about a week ago so it was all working fine then. The only items showing up were the three newly added ones. I rebooted my iMac and now it is fully empty - even the files I added a few minutes ago are gone. All that is available are a handful of tracks I purchased years ago from the iTunes Store but these are showing up as in the cloud and available for download, not as local files.
I can still see all the music files in the correct place on the SSD using Finder but they are gone from my library.
Any suggestions? Has anyone else experienced a similar problem? All the posts I can see on here about missing libraries are being told to look at the support page about sync library, but as I said, this is off for me.
iMac 27" 5K, macOS 10.15