I have the same problem. What I do is the minute it starts the video, I pause it and let it buffer 1/3 to 1/2 of the way and then start it. if it stops playing because you've reached the point to where it hasn't buffered, then your only option is to restart the video. This is very irritating, and I don't know why it does that. :/
lemme know if someone finds a solution, please!