Unreal Engine 4.26 Preview

Hi,
Strange things with raytraced shadows foliage in 4.26 preview 4.

I converted my 4.25 scene to 4.26 preview 4.

All seems to work well accept foliage shadows.
I have 3 grass meshes foliage scaled from 0.2 to 0.4.

When I paint these foliages, I have good raytraced shadows. But if I fill the whole mesh (Like i did with 4.25) I loose my shadows.
I tried differents ways. I changed the scale to 1 and retry to fill… all is working as expected with nice shadows.
So I scaled my original my fbxs to 0.2 and re-import them to fill with scale at 1. And no shadows…

Anyone knows what i missed…
thx…