Hi Aksu,
I believe it was only the cache causing the problem. Probably the query was executed before the import finished with the custom fields, and was cached without the artist name (as it did not exist at the time). I have turned the cache off for now: https://i.imgur.com/dpLPVN4.png
Let’s see if the issue re-appears again.
It should not make a big difference in performance, the database uses an own cache system, that should do the trick as well 🙂