Hi Jayd,
I'm sorry you're having a difficult time trying to watch the video. The video should play regardless of whether you have already watched it or not. I will pass it on to the technical team to look into.
But in the meantime can try using a different browser or downloading the video to watch it locally. I have personally had issues with browser extensions and add-ons that blocked CGC videos from playing, so try temporaily turning them off to see if it remidies your problem.
It might also be a long shot, but you could try pressing the "unmark as watched" button to see if your browser will then allow you to play the video.
Good luck. If you've made it this far into the animation course, I know you won't let a technical issue get in your way.