We have had some REALLY bizarre issues that seem to happen on computers other than the ones we tested on. Perhaps an issue with the HTML export or some oversights in how certain hardware would handle the game ¯\_(ツ)_/¯ But the downloadable version has been pretty consistent with performance and minimal game breaking bugs if you would like to experience it in the intended way!
You should check if your keyboard can actually detect those keys pressed in combination. https://drakeirving.github.io/MultiKeyDisplay/