Grafique card ? browser ? connection speed ? you have to give more info
Google Chrome, connection speed is quick and grafique card no idea
Try another browser , check adobe flash if updated or not , else : press windows key + R then type : dxdiag , click on display tab and check if your grafique crd is updated or not if dis didn’t help the ask Nick to look at your account
Safari is out of date and adobe flash player is up to date
I would try using a different web browser, or a different computer.
We are tracking this (rare) bug here: https://github.com/codecombat/codecombat/issues/1933