https://www.babylonjs-playground.com/#HHJFKL#1 hopefully shows the issue. Have StandardMaterial working fine, adding grid mat the instance is not visible. If it helps PBRMetallicRoughnessMaterial works fine as well.
Yep GridMaterial does not have support for instances. If you can create an issue for that on the repo I’ll make sure to make it work this week
Done:) will be in next nightly