Actor child SMesh not custom depth rendered throu post process material

Setup a actor outline material of my level post process volume, as a post process material, as shown in this video Custom Rendering Outline of Child SMesh Fails. - YouTube the child static mesh of my actor is not rendered, only the root mesh. If I set the child to custom render depth, it is ofc always rendered.

The post process material used is from this pack Action RPG Inventory System in Blueprints - UE Marketplace here I tried to change depth settings but without success.

Anyone an idea how to custom render actor child meshes through a post process material? Is there a special setting or material value needed?