Hi,
The message means your lightmap uvs are overlapping. I am guessing you are using the primary channel for lightmapping. You can solve that issue by creating a secondary uv set right inside unreal.
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To do this open the mesh inside unreal and then go to Window > Generate Unique Uvs. the default settings usually work well for this, so hit apply (you can tweak it if you wish).
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To view the generated uvs on the top you should see “UV Channel 0” change that to UV Channel 1 and click on the UV button that is next to “Additional Data”.
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If you are happy with the layout then go to the details panel and search for “Lightmap”.
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Change the “lightmap coordinate index” to 1 and the you can fiddle around with the lightmap resoulution.
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Rebake the lighting in your would and that should solve your problem.
Alternatively you can generate a secondary UV set in maya and then open the mesh inside unreal follow step 4 and 5 after you reimport your mesh.
Hope it helps. Sorry for the weird formatting, was just about to leave work. If you need more clarification let me know.
Cheers