A common problem with OrbitControls is that it hijacks (or “they hijack”) the mouse. This in practice disables dat.gui controls. The solution is to supply OrbitControls with renderer.domElement as the second argument.
The same applies to other testing templates, but I have not checked them.
I have to correct/moderate myself here. #17612 only gives warnings when domElement is undefined. So the change is safe for current fiddles. I suppose it may be changed to errors or exceptions in the far future.
The change will lead to breakage for all users of OrbitControls and TrackballControls since it’s not possible to apply a fallback if no domElement is defined. document is not valid for both controls anymore.