On my youtube channel I use Kimiko Ishizaka's open source bach recordings (under CC0) as background music. I got copyright claims every single time (from the same trolls -- forget their name). Eventually, when replying I got the idea to say, "You have made a claim on the same recordings for every single one of my videos. You have subsequently relinquished the claim when you discovered that I had a license to use this music. Given that you know that I have a valid license, you seem to be acting in bad faith. Please do not flag my videos again".

And, you know what? It seems to have worked. They never flagged me again.