I'm pretty certain this happens when the game isn't running in WebGL mode, which ironically can happen on newer devices more easily with the version of the runtime included in RPG Maker.
I had this problem too, since I was running the game using Proton and that doesn't give you hardware acceleration in a browser. I pasted the current Linux version of NW.js over it (adjusting package.json to have a non-empty name) and that was fine.