Quick answer: Unreal physics asset import resetting collision channels to default Pawn? Importer doesn't preserve per-body channel - script the channels post-import.
Re-imported skeletal mesh. Physics asset's per-bone channels (head, body, limbs) all become Pawn.
Post-import script
Editor Utility Blueprint: walk the physics asset; restore channels from a saved snapshot.
Or avoid re-import
For stable assets, don't re-import. Use Apply if only the skeleton needs changes.
Document the post-import steps
Wiki: 'after re-importing X, run script Y'. New contributors don't lose hours rediscovering.
“Importers reset what they don't track. Custom config needs explicit restoration.”
Build a 'restore custom physics config' script for each character. Re-imports become safe.