Hello,
The question above was concerning geometry LOD. But if you’re seeing leaves go away without geometry LOD happening, then you’re probably seeing the effects of mipmapping blurring the opacity channel and making tiny leaves disappear.
There are a couple settings you can change to affect this in UE4, but I’ve had good luck just setting the min alpha on the diffuse/opacity texture to 0.1. That’s below the cutoff threshold so it doesn’t affect things up close, but it’s enough of a bump on the low end to prevent tiny leaves from getting eaten away so much when the mipmaps are made.