It’s not a bug. Youtube deliberately throttles downloads unless the client can answer a math question.
https://github.com/yt-dlp/yt-dlp/commit/404f611f1c4aa516fbc4...
Of course this is easy to solve, but every layer of obfuscation they add generally requires someone to go and work around it in yt-dlp. It's mutually assured time waste on both sides.
I just learned an awesome new term. Thank you