Android Shadows Missing On Certain Objects

I thought that on my Galaxy S4 real time shadows weren’t working, and put it down to something in the hardware. Then suddenly one of my large helicopter models was casting a perfect shadow! However it only appears to be this one model that works, any idea at all why the rest aren’t working on the device when they are working fine in the Editor?!

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On the device only the Chinook shadow is visible, the trees and the ball have no shadows.

So it turns out I had a big quad (which was the base of my water) which I’d left casting shadows. When I turned the casting off on this quad (which was just below the surface of the entire terrain) the shadows suddenly appeared for all of the other objects. I guess that the big helicopter was big enough to grab some processing off the shadow system, but the others were ignored in favour of the quad which was shadowing terrain (even though it couldn’t be seen).