Seams on a side of a legs why? (Solved)

Hi everyone! Please can you explain to me nicely on what stage of my meshing/re-meshing annoying seams on the legs appears? Most of the time when I re-shape meshes or even just move/merge few vertexes on a sides or a bottom line of a dress or a skirt in-game check up shows me result with distorted legs(( How can I avoid it? Because even attaching a new legs from nude bottom or hiding original legs before transformation not always helps.