Lightmass crash: "Static mesh element count did not match mesh instance count!"

This error seems to have popped up out of nowhere (was running fine, then suddenly not) when attempting to build my lighting.

=== Lightmass crashed ===
Assertion failed: StaticMesh->GetLOD(GetMeshLODIndex()).NumElements == MaterialElements.Num() [File:D:\Build++UE4\Sync\Engine\Source\Programs\UnrealLightmass\Private\Lighting\StaticMesh.cpp] [Line: 277]
Static mesh element count did not match mesh instance count!

Running a geometry build doesn’t reveal any errors.

I can’t seem to figure out what the heck is causing it… any ideas on what it’s talking about, and how I might go about fixing it?

Thanks!

Solution was found here, under a different but similar error.

Hello Brittnell! I have the same problem, but it is not solved with the Swarm Agent! What can be? Thank you!

In case anyone has this issue and cant find an answer like I could not, to the “Static mesh element count did not match mesh instance count!” I figured out a solution. Hopefully this helps someone.

I accidentally auto generated an LOD so low, that it had 0 triangles, must have moved a decimal point. Anyway, once I re-did that LOD so it had some triangles, it worked perfectly.