Sorry for the nuisance. I assume you play on web browser directly on the site ? Or did you download the game ?
You seem to experience this problem on webm videos. I've restarted the game on my own, to see if something is off but everything works fine. The mains possibilites are : the browser can't find the directory, which is unlikely since webm are downloaded and not online / Your internet connection has a hard time displaying the webm.
Do you have the same issue on other games ? Or in this one, can you see webm in other panels ?
Feel free to send me your save, maybe there's something else I don't see.