Weird UVs issue on static mesh import

I’m experiencing some problems regarding mesh UVs.
In 3dsMax everything looks fine but once imported in Unreal some faces seem to have rotated uvs. I thought maybe I was doing something wrong, but I exported a higher resolution version (I simply applied “MeshSmooth” to the stack: EditablePoly > UnwrapUVW > EditPoly > Mesh Smooth) and the problem was gone:

http://s24.postimg.org/opkrnzvv9/Cattura_di_schermata_2.jpg

I also noticed that the low resolution version has some problems with smoothing groups, even though I properly set them up in 3dsMax and exported with “Export smoothing groups” option enabled:

http://s24.postimg.org/7nrxlwh05/Cattura_di_schermata_3.jpg

This are my UVs:

http://s24.postimg.org/havfvm9zp/Cattura_di_schermata_5.jpg

Any idea why this is happening? What did I do wrong?

Collapsing to editable mesh rather than editable poly solved the problem? Why? what’s the difference?

How did your modifier stack look?

Sounds strange.

I tried collapsing all, applying rest XForm, Mesh Smooth set to 0 but none worked (except converting to Editable Mesh). I reimported the .FBX in Max and found out that deleting the face and capping the hole solved the problem. Then I found this post (http://forums.cgsociety.org/archive/index.php?t-898928.html) where it says:

In my opinion that’s exactly what happened (this would also explain the smoothing groups problem). Converting to editable mesh maybe forces Max to recalculate (I actuallly have no idea what I’m talking about :wink: ) polygons orientation. Now I also tried reconverting to editable poly and the issue is gone.
If this is the case I just don’t understand why everything looked fine in Max before exporting.