Landscape crashes PIE in 4.20 on Linux

After importing several adjacent Landscapes into a level in Unreal Editor, it crashes trying to Play.
Reportedly both GPU and CPU have plenty of memory to spare.

If PIE is in the same window, it dies in
void ULandscapeComponent::Serialize(FArchive& Ar)
when trying to do // Duplicate shared reference
GrassData = (TSharedRef<FLandscapeComponentGrassData, ESPMode::ThreadSafe>)GrassDataPointer;

4.20 is smoking something since I don’t have grass, but ifdefing that out just makes it crash somewhere else.
Or, if PIE is in a separate window, it dies in
FPrimitiveSceneProxy* ULandscapeComponent::CreateSceneProxy()
when trying to do
Proxy = new FLandscapeComponentSceneProxy(this);

All of the Landscapes are visible (flight simulator) in the same level, so did I hit some upper limit for Landscape data in one map?
So far, I’m not using World Composition since the whole “world” is visible, but would Tiled Landscapes in separate levels be less crashy even though they would all be loaded up front?
Thanks for suggestions!