Steps to reproduce: 1. In Photoshop, create a puppet with art layers against transparancy
2. Rig the puppet in Character Animator. Do not add a background
3. Load the resulting puppet.chproj into an older version of AE. 22.1 for example.
4. Add the puppet.chproj to a comp and add a background. Looks great!
5. Open the AE created above in After Effects (Beta) v22.214.171.124 Result: The alpha of the puppet.chproj has a black border Expected: No black border. Not sure which app is changing how the alpha is handled, but this is new and unexpected...
Workaround: interpret the puppet.chproj footage with premultiplied instead of straight alpha.
System info Application: After Effects (Beta) v126.96.36.199 OS: macOS v12.2.1, RAM: 64.00 GB GB, CPUs (logical): 10