I play on Windows 10/Chrome. Game loads fine and everything works, but when I minimize the Chrome window and open it up again the game part of the window is blank (the ads etc are still there.) I get this error:

"An error occured running the Unity content on this page. See your browser JavaScript console for more info. The error was: Uncaught TypeError: Failed to execute 'shaderSource' on 'WebGL2RenderingContext': parameter 1 is not of type 'WebGLShader'."
Last night I tried the game in Opera and Vivaldi and didn't have this particular issue. Those browsers had other issues though, Opera used 60% CPU and Vivaldi kept freezing until it crashed.
Kind of solving my own problem. Apparently this is a Chrome problem that affects some people. Turning off "hardware acceleration" solves it, but CPU usage goes up. In Opera it's turned off by default, so turning it on makes the game run smoothly, for now at least.