HISM(Hierarchical instance static mesh) has lightmap problem after building lighting

HISM has lightmap issues after build lighting

• Create an Actor blueprint with HISM component added
• Add four staticmeshes instances, the default Cone for example. Move each instance around a bit to prevent them overlapping eachother in the BP
• Set HISM as static 
• Put the Actor in the viewport of a default level and build lighting
• After build, you will see the lightmap is messed up 

As a comparation Staticmesh actor or ISM actor has no lightmap problem; 

Previous version of Engine seems no problem

Tweak lightmass parameters in Worldsettings and build again fixed the problem, but aftere the second time build with same settings the problem is back again

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