Getting dark patches in baked light maps when baking with Final Gather in Unity 5.3.7

Hey guys,

we are creating a scene for web development and are working with Unity 5.3.7. But when the light maps are being baked with final gather on, the result has some patches. When the final gather is switched off, the baked light maps are clean. [See attached images]

The model has been created in Maya and the lightmap UVs have been generated in Unity.

Is this a bug or is there some setting that we are missing? Please help.

FG_On

FG_Off