I completely understand the frustration here as playback issues are never fun or easy to figure out.
It could certainly be an issue with Flash player.
You may right click on the video to switch between HTML5 and Flash.
You may note that you are having better luck playing the video using one vs the other.
It would be helpful to determine if this is a device specific issue and if you’ve tried to see if you may have better luck watching the video from the same connection but on a different device.
Also, if you can send me a link to specifically where you are watching the video, this may help.
And if you can, please visit whatsmybrowser.org and send me the link that generates that would be great as well.