Hi Alex, thanks for your response. I had tried doing these things a few times, but to no avail.
Oddly enough, I was just in my roon and adding a couple of new Qobuz albums to my favourites when, hey presto, the spinning blue disc started and my albums started to return! A few minutes and they were all restored including album artwork.
Not sure quite what made this happen, but I am a happy lad once again.