Feet Glitch

Hi. LODs differ from each other. The main difference is the polycount, but there can also be a different number of meshgroups and bones that affect the mesh. Your legs distort because of the latter. To solve this issue, you need to make proper LODs. However, before you do this, it is best to re-adapt your garment by transferring data from a skirt of similar length;
- append your skirt, delete all body parts from it;
- decimate the skirt;
- expand the rig, make nude legs selectable, duplicate them;
- select the duplicated version, remove doubles on it, delete all areas of it covered by the garment;
- in this order: select duplicated legs, Shift-select the garment, join;
- save the blend;
- File - Save as, overwrite LOD2, decimate the mesh further, save;
- File - Save as, overwrite LOD3, decimate the mesh further, save;
- import all lods into the skirt package, check in-game. If the problem persists, make LOD2 the same way you made LOD1

There are other issues, unrelated to this one:
- in MD model in quads, not tris. It produces a smoother looking garment;
- start a package from a skirt of similar length and transfer all data from it. It can be a bit longer but not shorter. Do not transfer anything from nude legs to skirts;
- skirts are vertex painted with two colors, not one. It is best to transfer vertex paint as well;
- your uvs in uv_0 are stretched. When you assign rectangular textures to uvs generated in square uv space, they stretch vertically. Before arranging them, you must bring them back to their original size ( S Y 0.5 );
- remove doubles on body parts