Weird moving glitch

Hi. Each meshgroup of your item must have the same vertex groups as the one it will replace. You transferred weights from an item that had skirt vertex groups but started a project from something that did not have them. Keep in mind that your outfit should also be split the same way the original is.
The second meshgroup of the outfit you cloned to start a package is a thumb. Why? No idea, I do not even see it in the region map entries.
Your outfit is not long enough to clip into boots, does not have collar or sleeves to clip into accessories, meaning it can be made from one meshgroup.

1). Select s4studio_mesh_2, Shift-select s4studio_mesh_1, press Ctrl j to join them;
2). Find b__CAS_L_EyeArea__ and b__CAS_LowerMouthArea__ in the list of vertex groups, delete both by selecting each and clicking on - button to the right;
3). Switch to Edit mode ( TAB ), disable Limit selection to visible, press B to activate box selection, select legs, press Ctrl L to select the rest of them, Remove doubles with Merge distance set to 0,0001;

4). Check the cut number, should be 0000, save;
4). Clone yfBody_DressPanels, import your blend here.

Also, do not combine the garment with the body until you transferred weights, a uv_1 map and vertex painted it. See how stretched uvs are in the arm area of your uv_1 map? That is the reason. There may also be inaccurate weights transfer in the finger area because they are too close to each other.
Your mesh does not need to be so high poly, you do not benefit from that extra definition in any way.
Do not triangulate the mesh when you're done, s4s will do it itself. Now you cannot select edge loops by just Alt-LMB-clicking on one.
And this is how you should vertex paint dresses or any other item with skirt-like bottom: