In the API you can have a single map instance utilized by several Views. This is great. In apps I've worked on we often have a 2d MapView and a 3D SceneView sharing a Map instance and running simultaneously in the browser.
A 2D MapView does not support 3D Layer types like ElevationLayer, BuildingSceneLayer, or whatnot. And the 3D SceneView doesn't support some other layer types like KmlLayer. Fine, makes sense. But, the problem is that instead of a 2D View recognizing standard 3D layer types and ignoring them (perhaps with a graceful warning in the browser console), it tries to add them to the view and fails, throwing errors like below:
Above example is with an ElevationLayer in a MapView. I haven't tested but assume simular behaviour w. incompatible layer types. (tested at 4.15)