Hey, go to your Video Manager in youtube (https://www.youtube.com/my_videos?o=U) and it will show you the copyright info for each of your videos. Click the "Matched third party content" or "Video blocked..." links to see details for a specific video.

I always put my mixes on youtube because the audience there is so much larger than soundcloud or mixcloud, but they get completely blocked around 10% of the time. Copyright stuff on youtube can def be frustrating, especially since it's so unpredictable.

The only advice I have is to keep your account in "good standing" w/r/t copyright and community guidelines (check here https://www.youtube.com/features) - you can get away with a lot more that way.