Weight paint looks good on blender but not working in game?

I've checked the file and there are a few moments that are not related to the issue you addressed but should be avoided in the future:


- when you close holes, make sure to not only shrink the selection but collapse it. This will reduce the polycount of the created geometry by half.

- when you delete the area of the body covered by the garment, you should put uvs in the freed space. You should always prioritize this space. In your case, there is more space there than in the extra area, so the uvs will be bigger and the quality better;
- and speaking of space, making the garment from smaller pieces will allow you to utilize it more efficiently. This ruffle at the bottom that makes a long uv island could have been split in two;
- when you paint the garment with two colors, you want there to be a smooth transition between them. You don't want the whole skirt to be painted with 3fff00 because it will morph very differently from the body underneath that is painted with 00ff00. So you can paint the top of the skirt with 00ff00, the rest of it with 3fff00, then smooth the transition ( Paint - Smooth vertex colors);
- if you were to look at the skirt in the object mode, you'd see dark shadow along the bottom and top edges. This will not only translate to ts4 but textures as well. You should split those sharp edges before baking textures and making the final import in s4s;
- you should do thinks like this: clone an item similar to yours, export the blend, open it, then import the obj from MD. The scene exported from s4s is set up differently, it contains the rig with body parts and its word settings are different, otherwise the texture bake will be too dark and ts4 may act up if the blend contains no body parts ( they are not imported in s4s but ts4 does not like when there is something wrong with them)