What is the best YouTube to MP3 Converter?

Is the video converted to MP4? That might be the reason. It also depends on what kind of converter you've used. Many of them add irrelevant stuff to the video, that causes bugs. Usually, those are the downloaded ones. That's why I choose to use online converters, such as https://convertr.org/avi-to-mp4. I never had any problems with online converters. Also, another cause would be how you added the MP4 to the video itself. I don't know if you're aware, but there are different ways you can do this. I usually just go to tools and then add, but many choose to complicate things, and it turns out like this, lol.