You will often find stuff in the engine that doesn’t make sense. I’ve found two methods that will give you results ( if no one answers your question ):
Do it another way
Cut out everything and put it back together one piece at a time. New project if you have to. Can you make a default level and get shadows everywhere? Is it the grass mesh? Is it raytracing ( probably not )? Is it the landscape? etc…
It’s weird that no one has an answer to this thing …
You put the grass alone without the foliage tool, and each piece has a shadow, but with the foliage tool, it completely changes the shadows, and it makes re-compiling, weird
When you can’t find anything else about a subject, and nobody answers, it usually means you’re the only one with the problem. Which also usually means, it’s peculiar to the asset or your setup, or just some weird project setting.
If you can make a minimal project with just a small piece of land and the grass doing this, I will take a look.