If you place the Elevator on glass and view it from underneath, the elevators become transparent/invisible from the bottom, but you can still see their sides? It's strange. View this screenshot to see what I'm talking about.

I like this bug, it's allowed me to give the impression that it's an elevator shaft, and it's not on that floor. That's just me, though.

The sides don't get rendered when viewed through glass either - made my fancy greenhouse floor a bit odd :D

It probably thinks that you're viewing it through a solid block, rather than a transparent block. Also, it doesn't work with leaves.

Can you try this?
It should fix it but when the elevator is camouflaged as glass it will show it's face when there is glass next to it.
In this image the top glass is a camouflaged elevator, the block below is a normal glass and you can see the extra face being rendered.

elevatorid-1.16.4-1.7.9-extract-me.zip