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Some faces from the UV0 for the texture UV are not used when repacking for the auto-generated Lightmap UV even if the faces are split and visible in the UV0.
Attached example mesh.
1. Import the attached mesh
2. Use default settings to that the UV is auto generated for the lightmap
3. Add static mesh to a scene and build lighting
Results: Some faces will not be in the repacked UV for the lightmap
Expected: all faces should be repacked whether they are split or not.
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