Ok, I think I have narrowed it down to the ShapeDiverDisplayGeometry forgetting the color.
Here is the same model, but I am not using the ShapeDiverDisplayGeometry: https://app.shapediver.com/m/piano-keys-no-color
It stays visible all the time.
I have noticed the same behaviour in 3d-models, that sometimes the material-input of the ShapeDiverDisplayGeometry needs to be reminded of what color it should show.
It’s not visible in top view, but your model contains several instances of the same piece of geometry. It can be easily seen by witnessing the flickering that happens if you disable the top view.
Anyways, this probably means that you have not disabled the preview for some components in your definition. I am guessing that in your second model, you just deleted the display component but kept its parent visible. Make sure you disable the preview for everything except the ShapeDiverDisplayGeometry components.