Haha, no I’m not gonna leave you hanging on the solution.
Epics answer to this problem is set material by name, this lets your BP assign the correct material to your mesh regardless of the material element order. And this works fine, if your BP only uses one set of materials for everything.
(This is for Maya users as I use Maya)
If you really need to set the material element order for you meshes group and have them all have the same order.
You need to separate your mesh by material, so each part only has one material assigned.
Group your parts together in the Outliner and then arrange the parts in the order that you need. Export it.
On import to UE4 tell it to combine meshes on import and now you will have a mesh with the material element order that you set in Maya.
