Usual fixes for weird cloth sim issues:
-Make sure everything has their scale applied (ctrl + a, set scale)
-Parent the cloth to an armature bone, not the mesh of the character
-If it is parented to a bone, ensure only the bone you need is in the vertex groups and not a bunch of needless others (the menu with the green triangle, you can see all of your vertex groups associated with the cloth there)
If none of this works I'd have to look at your blend file