How to create world to work cross platform

Hi

I'm new to Unity and I am creating a scene (world) where all my objects are put (player, other objects, obstacles, etc).
I create almost all my items in runtime (programmaticly) due to data is fetched from external repository.
Everything works like charm when being in Unity and exporting it for example Windows but when I export it to Android apk and run given game on my device (android) coordinates seems to be all wrong. Player is not set on game plane and is falling down, its another behvavior than in Windows-export..... I thought that Unity was a facade so if it works in unity it will work in other devices (exported correctly).... I dont know if I have missed something here or what I should do to minimize risk that exported versions (android/windows/Iphone) have different behaviors....

Would be very happy if someone could help me to explain what to do or what I have missed.... Maybe this is the way it works and then I wonder how should I create "the world" and "all items" so they are transformed correctly independently of device/os

Thanks for your help!