Hey there.
I tested this on my trees as static mesh, single instance foliage, painted foliage and procedurally generated foliage and they all behave the same. I think it must just be unreal engine changing the way they do things behind the scenes all the time requiring a bit of tweaking. My game is a giant forest of painted and procedurally generated trees and all the imposters work perfectly now, and static mesh versions of the trees also behave the exact same way despite the material using “instance and particle space”.