Hey there.
Trying to use the RuntimeMesh with Outliner in Materials - UE Marketplace. This material uses CustomDepth (Render CustomDepth Pass / CustomDepth Stencil Value) to create the outline. It is working with the RuntimeMesh as long as the RuntimeMesh is not fully Occluded (The ProceduralMeshComponent has issues as well, behaves even weirder than RuntimeMesh).
Screenshots out of Editor, not playing.
Blue Outline = StaticMeshComponent
Green Outline = RuntimeMeshComponent
Partially Occluded:
Occluded but RuntimeMesh (Actor) still selected:
Occluded, RuntimeMesh not selected:
Maybe this is related to the issue of Dustums:
You can also check this by using the render options with the editor viewport:
A related thread for ProcedualMesh: Render Custom Procedure Depth Doesn't Work - Rendering - Epic Developer Community Forums
Regards