Why does the game work on some devices but not others?

It could be anything. First things first, is it browser-related? Some browsers are better at handling games than others. Have you tried Chrome or Firefox to see if it’s consistent? It could be a problem with the hardware of the device itself. Perhaps an old laptop cannot cope with resource-hungry games. Or it’s the GPU drivers, or maybe even the OS update. It might not be designed to run as a mobile app. And maybe you’re using Flash or WebGL which may not work on all platforms. I’d test across a range of devices to see if the problem remains. If that’s too time consuming, advise users to update their browser (or use a different browser). Start narrowing it down, it’s probably a question of either performance or compatibility. Let me know how it goes.

Browser problems can’t be ruled out - each browser has its own way of handling scripts / web sockets / websites, etc. You might want to try it with different browsers (Chrome, Firefox, Edge, Safari....) and also consider old browsers and/or operating systems. Device capability is a factor that you may want to rule out - cheap devices will crash if they have to run a heavy game like this. Try reproducing it on various devices. If you’re using WebGL or HTML5, older graphics cards won’t work. Ask your users the OS/browser info - that’s where I’d start.