Custom top doesn't work properly in game

Blend (before importing to S4S) needed to pinpoint a problem. The only thing from exported from .package .blend I can tell that a lot of vertices on your mesh got assigned to index fingers.

Alright, this is what I thought. Whenever you use Blender 2.76 and up for weight transfer it creates a lot of empty bones, 2.70 doesn't do that. You need to "CLEAN" step from this tutorial and then change from "active" to "all groups" in menu on the same tab. Then I advice to select all vertices again and press "Limit total" and put 4 in a menu below. Game reads 4 bones per vertex, so if your mesh has 5 bones assigned Studio throws off some weights. I always do this step just to avoid additional glitch.

you have to scroll up or move the scroll bar up that little "keep single" box. what you need is above that.

as for the limit, probably no vertex has more than 4 to start with. so nothing was in need of change. I'm assuming, can't see the file right now.