Leaves on tree create blocky shadows

Hi there,
I’m very new to Unreal and after experimenting a bit I started creating and importing my own assets.
Unfortunately I have a big problem when it comes to the shadows on my static tree meshes.
I use Alpha textures for the actual leaves and in the preview everything looks as expected:

But when I build my lighting it starts looking like this:
I couldn’t figure out why this happens. I used the production quality when building and cranked up the lightmap resolution (128, 256 and then 1024)
Still blocky.
I’m using a directional light in this scene.

Does anyone know why this problem occurs and how I could fix it?

Set Directional light to use Area shadows.

Increase your lightmap resolution on the ground, if the ground is made from BSP then you need to decrease the number–note that shadow resolution is controlled by the object receiving the shadow.

Thank you that fixed it for me. Kind of obvious solution in hindsight.