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this is not a dupe, but can be closed because it was answered in the other one.  It was fixed with the forward / deferred setting.
nothing right now.  Go ahead and close it.  I'll just let you know if it happens again
Thanks for the info Lionel.  I was thinking the same thing, but that sounds crazy at the same time.  But I guess it's not that crazy after all! :)  I'll give that a go.  Hopefully it will work if my mesh is being used on a terrain.

thanks again!
I simply duplicated and dragged the mesh around the scene. as for the extra node, what all I did was add a lerp to assign which source the vertex channel should use because you use blue and I use green.  it was just to make my life easier while testing the two meshes.  Once I added that it started working, then I removed it and it was still working.  The other thing I did was re-export my mesh with scaling that was closer to what it should be, but I don't remember at what point I did that and if it had anything to do with it working.
ok, so after some more testing, I can confirm that your mesh is also broken. But it was only seemed to occure when I put several instances of it in a bunch.   I just added a new modifier to the shader and recompiled it and for some reason it's working now.  Something fishy is going on.  I'm not 100% convinced that it's building it properly.
I just tried your example shader with my mesh and I get the same problem.  but if i use your mesh with my shader it works like a charm.  I guess the problem i'm having is in my mesh. hmmmm.
it looks fine in the example scene.  it really seems like the mesh has some other shadow caster that's not matching it.  the movement seems to be much larger.
as a side note - it's hard to tell because I'm relying on vertex colour to attenuate it, but it seems that if I use a built-in plane it works fine.
it was not.  I just fixed that and it got a little worse.  now my shadows have a strange dithering effect going on.  BTW - i was in DX11 mode and turned that off as well.

I should say though - after doing this I can clearly see that my vertex animation is set to move in sin along the X but the shadows are moving in sin along the Z.  To clear that up - in this image the leaves are moving left to right but the shadows are move back and forth.

i tried setting to forward. the result is also bad.  I see that it's cutting out properly, but It's not updating the shadow pixels in the same direction as the albedo pixels.  so you get the is crazy look of "invisible" leaves over the rendered leaves.