Fading out transition with...dark elements?

Hi all,
I’m a beginner who’s trying to do a fading out transition in a couple of geometries in my scenes; In short words, I have a home and I want to make slowly invisible all the floors except the central one, to zoom on it later to show the furniture and the rooms.

The effect works, but the other floors release a short of “dark wireframe”, like their own shadows, even when they’re not visible anymore.

Has anyone faced something similar?
I can’t upload pictures as it is a work for a company, I can just say I faded out the floors using a mix shader with transparent BSDF in the node editor for EACH material (glass steel…) and to create some parts like the roof and the top floors I used a Boolean cut, and then merged them (as the roof is 30 degrees inclined).

Maybe the problem is due to some “extra” parts I copied but didn’t delete, without any assigned materials; they are on the same position of the originals and overlap them, which makes even more difficult to erase them.

Any suggestion or similar experience is welcome.