CrystalGipsy,
The conclusion was - perhaps too obliquely implied - in this post.
I had ProStudioMasters make available a fresh complete download of Handel’s Semele. Importing that fixed it immediately.
I agree that a section in Roon somewhere which scans the database and reports any corruption - if there is any (which I do accept may not be the case for you, honest 
) - would be very useful.
Where have you found that - actually in Roon, CrystalGipsy, please?
What did you look for and in which log?
Sure! I agree with you, though - please remember - that corrupt files may or may not be the cause.
This is what they wrote:
…We reviewed a fresh set of Roon Server logs from your device and found log traces saying quite literally “Possible corrupt file” in the logging…
I don’t remember seeing that myself in any log. So could it be that this diagnosis procedure/tool is indeed only available to RoonLabs staff.
May I ask you to describe what you did exactly, please, CrystalGipsy, please: that could add to our knowledge…