Could it be possible if (on whatever device this bug occurs on), you make a reply to this topic and press the black-n-white globe icon which is right next to the emoji icon? (It provides us some information regarding your device and browser, which might be helpful)

A screenshot of the stage not updating would also be nice. Make sure to check that the costume of the sprite isn't blank (or really far out from the center), that the sprite has a large enough size to be seen, and that the x and y location of the sprite isn't some absurd value.