Hey!
I just want to share a small tip that can save you a ton of time.
I never explicitly provided the optional scene parameter when creating objects on the scene—until now…
Since introducing a new scene (both scenes are initialized asynchronously) their contexts started to mix.
Now, I have to review every function call that accepts an optional scene parameter and explicitly pass the correct scene. 
Explanation:
If you don’t provide the scene parameter to a function that supports it, Babylon.js retrieves it using the LastCreatedScene static getter from the EngineStore class. Since it is static—you get the point.
public static get LastCreatedScene(): Nullable<Scene> {
return this._LastCreatedScene;
}
So, take your time and always specify the scene. You never know when it might save your bacon!
