Unable to add Screenshot to game

I am teacher working with a group of students. Most can add the game screenshot like it says under My Games. However, one student does the same process and the ability to add the game screenshot does not appear. I have tried it on different computers (Laptop and Desktop )S 10.9.2 and different browsers (Chrome and Safari).
This is the game. https://flowlab.io/game/play/74987

Is there a fix?

A fix has been tested and deployed, thanks for the report!

Thanks grazer