Hi. The body contains too many bones, remake it.
- clone a swimsuit made of one meshgroup, export the blend, open;
- append your bird costume in this scene, delete rig.001 and bone_bone_shape.001;
- select the swimsuit, in Edit mode select everything with A, Mesh - Merge - By distance;
- enable X-ray, select and delete all areas of the body covered by the bird;
- select the bird, delete both color attributes, create a new one with black. Can delete uv_1 as well;
- in this order: in Object mode select the bird, Ctrl-select the body, join with Ctrl J;
- make sure the cut is 0000, import back into the swimsuit, do not re-use the old package
It worked! Thank you so much!