Information : The 3D grass is only available for Artlantis 2019.
Issue detected : You applied the 3D grass shader but it doesn't show up in the preview.
Cause of the issue : Due to software speed reasons, the 3D grass will only be calculated for renderings.
How to solve it : Once the 3D grass applied, run a rendering and check the result. If the grass is still missing, it is very probable that faces were reversed in the modeler and the shader was applied on the negative side. First, you'll need to change the orientation of these faces and reapply the shader again.