Ok, please avoid to use the Mix Material, and prefer to use the Composite Material instead.
https://docs.otoy.com/cinema4d/CompositeMaterial.htmlMix Material has several limitations in C4D, works only with 2x materials, it needs to work in conjunction with 2x other node materials so it is difficult to move it in another scene, it doesn't work in C4D Content/Assets Browser, and doesn't work correctly with Solo mode.
Composite Material solves all these limits, and it works correctly with Solo mode too.
If you select a Mix Material in Material Manager, then go to Live View menu Materials/Convert Material, it will be automatically converted into a Composite material
Mix Material is obsolete and available only for retro compatibility.
But for leaves and grass, my suggestion is to use an Universal material, to be able to work with one single material with all the necessary characteristics, and in this way, you can change the Transmission type to "Thin Wall Diffuse", perfect for leaves and grass blades:
ciao,
Beppe