Does it happen in a particular browser?
Thank you for the response.
If there is no response for the bug report, try these steps
1. Try a different browser and also clear the browser's cache and cookies.
2. Try to disable hardware acceleration.
3. After updating flash player, did you try to play the videos in high quality; 480p or 720p?
You can also try a new User account and let me know if it helps.
Do write back with the results.
Thanks and Regards,