Hybrid Render with WebGL only works with ConvertToEntity

I have been trying to use Hybrid Render with WebGL builds. It works fine when the ConvertToEntity component is used, but not when adding with entityManager.Instantiate(prefab). For example in the ECs samples HelloCube, Foreach and IJobChunk work in WebGL builds, but the three Spawn examples show nothing in WebGL builds. Is this just a feature not yet implemented or could it be something wrong with my build settings?

Cheers,
Grant