Tested with the default Ultra INIs, no luck there. Disabling DynDOLOD's output files makes the snow appear as you'd expect from the vanilla LODs.
Noticed glancing again at the meshes that the LOD4 mountain's BSSubIndexTriShape has the name "objSnow-LargeRefobjSnowHD-LargeRef", which doesn't quite look right? But I'm not sure if that's anything.
meshes.zip