For some reason, the
environmentBrdfSampler texture of the material is wrong when you create additional scenes (I compared a snapshot with Spector of both cases).
After comparing a
environmentBrdfSampler in both cases, the only notable difference is that
glass.environmentBRDFTexture._texture.onLoadedObservable._observers array has 11 elements in the wrong case and 1 in the other case, meaning as many elements than there are scenes.
If you do:
to retain only first element in the wrong case, you get the right display.
Now, why is that, only people knowing inner working of the engine will be able to answer.
Note: of course, you should not tamper with private properties, I have only done it to show my point.