1. What happened

Using automatic weights in the skinning editor for 2D PSB character rigs assigns vertex weights to the incorrect bones in Unity 2021, while it assigned the correct weights in Unity 2020.

2. How can we reproduce it using the example you attached

A. Navigate to the skinning editor of the "Rig_Leg" PSB file.
B. Select "Auto Weights" and then "Generate All."
C. Observe how the weights are assigned incorrectly.

3. Notes

The above repro process has already been done in the file, and the incorrect weights can already be observed.

4. Unity 2020 test versions used

Unity 2020.3.33f1
2D Animation 5.2.1
2D PSD Importer 4.3.0

!subdivide-settings.png! -------
Additional information (20 May 02):

Repro:
- import .psb sprite
- Open in skinning editor, rig it with bones and auto-geometry to set up with weights
- Edit / add / split bones to change the bone structure
- Generate Auto-geometry with weights again
- Note that the weights are not updated to the current bone rig structure

Weights aren’t updated when invoking auto-geometry with weights). Weights are only properly updated when using Auto-weights with “Associate Bones”

Refer to video demo "AutoGeometryNotUpdateBones.mp4"
[^AutoGeometryNotUpdateBones.mp4]

Observed on 2020.3.34f1 / Animation 5.2.1