Hey!
A bit of an late reply, but I figured I’d answer this for anyone else facing this issue.
So, I also had the same issue. Carefully creating the normals on my mesh, and they would look incorrect whenever it was turned into a wardrobe item (and checking it in my Metahuman creator screen).
Now, the reason this happens is actually because the Outfit asset (which is what’s being used by the wardrobe asset) essentially combines the simulation mesh (Sim mesh) and the render mesh together, combining essentially the normals together.
If you don’t create your own simulation mesh, and have UE essentially figure it out, this can create these odd shadows since it’s trying to use your render mesh as a simulation mesh and doing some modifications under the hood to make it sim-ready essentially.
So, how do you fix this? And how do I make a sim mesh? Well, it’s pretty easy! Essentially all the parts you do NOT want to animate (Which in your case is pretty much the whole mesh) can be super low poly.
Any hard edges, seams, buttons, bows, details, etc. you want to remove. Essentially you’re creating a dumbed down version of your mesh. the sim mesh is really just the for physics in the end 
Then, in the ClothAsset you want to add 2 nodes (SkeletalMeshImport = Render mesh and StaticMeshImport = sim mesh). And then merge those 2 together with a “MergeCollections” node. Then continue on as usual (transferWeightsNode > ClothTerminal)
Test it, and voila! You should be able to see any weird shadows as well in the Outfit asset screen too, but it’s a bit less visible. Doing this is also much better for optimisation reasons as well, since you know which bits in the sim mesh needs more polys for a better drap/flow, and what areas don’t Therefore meaning UE has less vertices to calculate!
Here’s a quick example from one of my dresses on the fab store. The original mesh has a turtle neck, where the fold is on the outside.
If I were to keep that in the sim mesh, it would create really odd shadows. Now, by essentially creating a merged variation and making those details less complicated I don’t have those shadows 
In the end it’s good to note that this issue really is only in the Metahuman creator screen. Usually in your actual game it uses your proper helmet’s normals. I’m not entirely sure why it does that but that’s just been my observation.
Hope this helps you and anyone! I really just figured it out from trial and error.
Is there any way to prevent MetaHuman Creator from recalculating or modifying normals/smoothing groups on wardrobe assets?