We'd like to help. Is this on videos that you've uploaded or someone else's videos? Also, have you tried to check if it's the same across devices? Let us know.
That's odd, could you file a feedback report with these steps: https://goo.gl/1ckkO5 ? We review all the feedback sent to us, but YouTube doesn't necessarily respond to every single one. We use the info to identify and fix issues, as well as track requests and make improvements.