Hey! Sorry you ran into this issue, I had the same problem when I first uploaded the game, and it's due to performance, I have since added a lot of performance fixes and it seems to run pretty good on most machines. Just make sure you have graphics acceleration enabled on your browser, I was able to re-create the issue still when I turned mine off.
I unfortunately was not able to find any other settings to help with this issue, next time I will make sure to have an option to download the game to play out of browser as well!