This repro case demonstrates the problem.
`UMyBlueprintFunctionLibrary::ReproduceIssue` does `PrepareGeometryExportSync` and then kicks off a task that calls `GatherGeometrySlice`. This will crash in `FReproGeometryExportClass::ExportChaosHeightFieldSlice` if called while the camera is being jumped around to provoke streaming.
The level blueprint will trigger the issue if you play the ReproMap in editor.