well, I'm unable to find a solution by myself.
I'v tried to make a minimal example showing the problem. There are two projects, one for Windows DX and another one for Android:
Drawing functions and setup are at common/GameFuncs.cs
Shader is inside the shader folder. The original shader is in PointLight_DXY.fx, while FaultyFunc.fx contains the functions for a test shader in order to make the shader fail commenting one line (technique #4)
I am compiling it directly with 2mgfx (there's a batch script in the shader folder)
Basically the point light vertex shader works on Windows but not on android. The Faulty file contains a function which still works on Windows DX (it has several instructions removed so it's not making what it should do) but it does not work on android. However, if you comment the line after "COMMENT THIS", the shader works. (by "not working" I mean that the geometry disappears,showing just a CornflowerBlue screen)
Thanks in advance.
p.s. My shader knowledge is very limited. Sorry if the code hurts your eyes