I've been getting 1960s public domain Atomic Energy Commission films scanned from 16mm reels at the National Archives and posting on YouTube. I noticed they were running a lot of ads even though I had monetization off. Turns out, each one got a few copyright claims from people who apparently release "remastered" old music in the 2010s. I got annoyed and disputed them all and as of yesterday the claims have all been released. What a pain.