When using the “CustomBrush_MaterialOnly” blueprint on a landscape via the landmass plugin, with a material instance attached to the “Brush Material” slot, changes to parameters in the attached material instance do not dynamically update the landscape heightmap in real time like a material instance would when applied directly to a mesh.
Parameter changes in the attached material instance only seem to apply after a change is manually forced to the landscape, ie changing one of the transform values or exiting landscape mode seems to force a fresh load of the material instance.