Yup, I was having the same issue. Procedural Foliage Volume was not placing foliage types that specified a landscape layer ( to use as a mask ).
The solution/ workaround that I found was this:
The first landscape level/tile that you place using world composition can not be moved from its original placed default position in the world composition window.
If you don’t shift it, the Procedural Foliage spawner volume works as expected with landscape layers. If you move the original tile, it does not work. Thankfully, if you shift it back to the original position, it will once again function properly. Additional landscape tiles that you create after the first one can be shifted around as much as you want.
Unreal seems to be using the default starter position on the first tile as the cornerstone for however it interprets landscape layer masks.
