To be able to scale to fit any screen size, my game uses the setup shown here (scaling for a single page) : https://www.yoyogames.com/blog/67/scaling-for-html5
It works perfectly if I just run it in browser from Game Maker, or from here: https://cthulhucreates.github.io/FetchQuest/
But where it's uploaded to itch (https://clockework.itch.io/fetch-quest) it doesn't.
The game was built in Game Maker 1.5, I'm using Chrome, I've tested it on several devices.