Need weight help with a full-body frankenmesh dress

You do not need to split the outfit into meshgroups, but you need to clone something that has the same number of meshgroups and is affected by the same vertex groups. Clone DressPanels instead and import your blend there.

The issue you are witnessing is caused by the fact that you replaced a mesh not affected by skirt bones ( and possibly breast bones) with a mesh that is affected by them. You do not need to clone other creator's cc to make your own, and if you did not, please do not rename the package (Xyzzy_Aveira_Wednesday Dress_), we need to know what you cloned to identify the problem.

Also, you can delete all bone_bone_shape and rig.001-016

Do not use Make blank button, it removes maps from the file thus disrupting its structure.