Problem with shadows on my grass

Hello everyone, my first post here.
I’m pretty new on UE 5 and for my first project on it I create a penthouse.
But when I use the foliage mode to paint grass, I got a problems with shadows who disappear from my grass if there are too much instance of it. There are still part with shadows but one meter on the right, nothing. I found many post on shadows who disappear far from the camera, but here, even if I’m close, there still nothing.

I did a quick video to explain my problem.

Hope someone can help me ^^ (and sorry for my globish).

Try do disable lumen global illumination and reflections, if that fixes your issue, it means it’s something in the light bounce settings, I guess there are some reflections/light bounces involved as once you’ve added a uniform layer of grass it gets treated like a surface. I am new too so I am just taking a guess.