HISM has lightmap issues after build lighting
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
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-62526 in the post.