World Partition Mesh actors fail to load in PIE

Summary

When entering PIE in Unreal Engine 5.8.1, my Mesh Terrain disappears. The collision from the terrain remains, but the meshes never stream in.

I have done the following:

  • Set up a Mesh Partition Definition
    • This MPD includes all of the Device Profiles and other assets from MPD_Default
  • Compiled the Mesh Terrain

The Mesh Terrain appears as normal when outside of PIE. I have ensured Nanite is fully functional. The terrain is a default Mesh Terrain square and three Static Mesh Boolean Modifiers.

My hypothesis: when loading in PIE, the Collision asset shows in the Outliner, but neither of the compiled Static Mesh profile assets show, leading me to believe that the absence of these assets during PIE prevents the terrain from loading.

What Type of Bug are you experiencing?

World Creation Tools

Steps to Reproduce

  • Create an empty open-world map with a Sky Atmosphere, Directional Light, Volumetric Clouds, and a Skylight
  • Add to this a default Mesh Terrain square, with three Static Mesh Boolean Modifiers
  • Duplicate the default MPD and add your own material
  • Compile the Mesh Terrain
  • Load into PIE

Expected Result

The Mesh Terrain should appear exactly as defined in the Mesh Partition Definition, and as it does outside of PIE.

Observed Result

The Mesh Terrain does not load, and you are left with an empty black map with collision. The Compiled Collision asset loads, but neither of the Compiled Device Profile Static Mesh assets are loaded.

Affects Versions

5.8

Platform(s)

Windows