i had a charachter wearing short which i converted to a skirt. in doing so i added new vertices/ edited the existing ones.

when i go into pose mode some of these new or edited vertices remain completely stationary, regardless of what the rest of the object is doing. see image below for example.

[![enter image description here][1]][1]


when i go to edit mode, everything snaps back to a default position so i cant tell which vertices are even the problem. how could i interogate the vertices in the image below to find the problem causers? i know roughly which ones they are but thats not good enough?

[![enter image description here][2]][2]


  [1]: https://i.sstatic.net/d6m7R.png
  [2]: https://i.sstatic.net/0tc6C.png

also how would you recommend i go about finding the problem here?

extra info:
this was object was made with vroid and imported into blender as a vrm. 
it all worked fine before i messed with it.