Mesh Terrain just not working

Summary

Mesh Terrain unsuable - takes forever to load on a basic rectangle and when trying to play in standalone crashes on an empty mesh terrain map.
Assertion failed: ComponentNativeClass [File:D:\build++UE5\Sync\Engine\Source\Runtime\Engine\Private\WorldPartition\WorldPartitionActorDesc.cpp] [Line: 913]

What Type of Bug are you experiencing?

World Creation Tools

Steps to Reproduce

make a basic terrain mesh landscape and just press play standalone.

Expected Result

it should load - mesh terrain just doesnt work.

Observed Result

crash

Affects Versions

5.8

Platform(s)

Windows

What I have done…

I know that this shouldn’t make a bit of difference, but have you tried it with an imported heightmap?

Have you set your World Settings to be loading your Game Overide Setting?

Is there a PlayerStart loaded onto the map?

I have successfully imported a 8k map and ran across some of it. Runs like crap but it works.

Did it work in standalone?
I get the same error as OP when I try to standalone play (both PIE and Packaged) a level that has a mesh terrain in it

Got the same crash with StandAlone.

Also just in PIE the landscape always has visual arifacts, like holes. I think because of nanite

Managed to get standalone working after making sure that all plugins were set properly, removed saved and intermediate. Launched the engine from EGS, which installed prerequisites for 5.8.0. Then relaunched my project and packaged again. Now the levels with a Mesh Terrain load correctly and work fine!

On this Discord thread we had a discussion with Roey about the PIE standalone issue and he was able to replicate.