The videos repeat, and when they do (for me they repeat every time) the screen is just dark-gray. I have to reload the page to fix it. Also, rewinding/skipping ahead to a previous point on the video is a hassle. I often land about 30-40 seconds behind or ahead of where I wanted to start watching.
I can confirm that I had this issue too. Desactivating Adblock on GB seems to have fixed it. Not sure.
Here's another issues: There's stuttering and back tracking in the videos and having the same audio play before the visuals speed up to catch up. (Quoted from another thread)