Following code fixes this issue

in FQuadricSkeletalMeshReduction::ReduceSkeletalMesh

						Section.ChunkedParentSectionIndex = bIsChunkedSection ? CurrentParentSectionIndex : INDEX_NONE;
						//If we reduce inline the source model, we want to use the real source original section
						Section.OriginalDataSectionIndex = bReducingSourceModel ? SectionData.OriginalDataSectionIndex : OriginalSectionIndex;

						if (!bLODModelAdded)
//							if (FSkelMeshSourceSectionUserData* BackUpUserSectionData = BackupUserSectionsData.Find(SectionData.OriginalDataSectionIndex))
							if (FSkelMeshSourceSectionUserData* BackUpUserSectionData = BackupUserSectionsData.Find(SectionIndex))
//								FSkelMeshSourceSectionUserData& ReducedUserSectionData = ImportedModelLOD.UserSectionsData.FindOrAdd(Section.OriginalDataSectionIndex);
								FSkelMeshSourceSectionUserData& ReducedUserSectionData = ImportedModelLOD.UserSectionsData.FindOrAdd(SectionIndex);
								ReducedUserSectionData = *BackUpUserSectionData;

						SectionMatched = true; //a backup section can be restore only once


Steps to Reproduce
  1. Open a skeletal mesh asset which has multiple material section
  2. Increase Number of LODs and press regenerate
  3. Make sure the last level LOD has fewer material sections
  4. Select the last level LOD and uncheck Cast shadows options
  5. Press regenerate


Some cast shadows options lose their settings

[Link Removed]

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Cannot Reproduce
CreatedNov 25, 2020
ResolvedApr 28, 2022
UpdatedMay 5, 2022