I had a suspicion this already happened in the past but now I’m sure: a few albums I added a few weeks ago and listened to in full are now… as per title 
Roon Server running on a dedicated 2012 quad-core i7 Mac mini (macOS 10.13.4)
Files on a Qnap HS-251+ NAS
Hello @pl_svn,
Do you have Roon backups enabled? Are you able to roll-back to a previous version of your database to see if the edits are still there?
-John
hi john
yes, forgot about those: rolled back to the oldest backup I have (May 25th) and my edits are there 
then rolled back to a more recent backup (May 31st) and edits are still there too
nonetheless… ???
I had a similiar problem.
In the last few weeks two times an album from Tidal are missing from my collection.
The albums are available in Tidal and I could readd them without a problem, but all edits are lost.
Maybe more albums got lost without me discovering it yet.
no idea what happens when removing then adding anew files from a streaming service: files I’m seeing this happen with are all local and available to Roon all the time
Hey there, @pl_svn!
Glad to hear you’re back up and running!
I have enabled diagnostics on your account so our technical staff can get some more insight into what may have happened. The next time your Core is active a diagnostics report will automatically be generated and uploaded directly to our servers.
I’ll have the technical team review the report and I’ll be sure to let you know their findings.
Happy listening!
Regards,
Dylan
thank you Dylan
really curious to get what might be the cause as, as I wrote, I have a strong “feeling” it is not the first time it happens