It occurs if you minimize the game then full screen it again, or if you wait until it's loaded to full screen it. It basically just shows the loading bar.
Viewing post in Beneath the Dreaming Sea jam comments
Hmm ok, i tried it a few times now. In Chrome seems no problem at all. In Firefox i saw something similar what you describe, but game seems to continue when you click with the mouse on the screen. Is that the same one you meant?
Definitely shouldn't happen, i'll check out, thank you for reporting it :-)