Off hand I would say you lightmap is to small. Default is 32 so try bumping it up to 64.
Also something to keep in mind is when you scale anything in 3ds Max using the scale tool you only scale the relative size of the object relative to world scale. The local scale of the object does not change so if you make a box 10 X 10 X 10 then that scale will always be set no mater how big you make the object, say the size of a building.
This is important as engines these days do use real world physics and lighting solutions that normally get the seed value base on the local scale of the object and if the local scale does not match the relative scale you can get unusual lighting or physics results.
As a habit either add an xform modifier to the stack before scaling, which translates the local scale to the relative scale or use the xform rest under utilities tab.