Spine IK Stops After a Skin Swap? Check Constraint Membership

The arm is visible after a skin swap, but its IK target no longer drives the pose. Save a small reproduction with a fixed target and animation time. Attachment visibility is one observation. Whether the constraint can act on the active bones is another.

Build a membership matrix

Use the official reference to list the constraint, its target bone and the bones it modifies. Add their skin memberships beside each name. Start with a skin-specific target and check that the constraint belongs to the same skins. When every constrained bone is skin-specific, also check the documented requirement for the constraint to belong to a relevant skin. Do not infer membership from the outfit that happens to be visible.

Test one skin at a time

In a copy of the project, unpin other visible skins and reproduce the intended exported skin on its own. Record the target position, constraint mix, active bones and tree warnings. Correct the membership according to the guide, then repeat the exact pose. If IK now acts but reaches the wrong position, preserve this result before investigating coordinates or constraint order.

Check the transition directions

Run A to B, B to A and a fresh load directly into B. A failure limited to one direction calls for a runtime skin-setting and update-order trace. The related diagnostic guide provides the separate bone-activation checks. Keep the matrix, runtime version and failing frame with the handoff. Review compatible asset appearance in the Spine Workbench, and verify the skin constraint behavior in the receiving engine.