How to Fix Unreal Runtime Retargeting Stretching the Arms Because the IK Rig Chain Mapping Is Wrong

Retargeting animation from one skeleton to another at runtime relies on IK Rig chains lining up. If the new character's arms stretch, the chains are mismatched. Here is how to fix the mapping.

How to fix it

1. Define chains on both IK Rigs

In each IK Rig, create retarget chains for the spine, both arms, and both legs spanning the correct start and end bones. The Retargeter can only map chains that exist on both sides.

2. Set the retarget root

Choose the pelvis as the Retarget Root in both rigs so translation is handled consistently. A wrong root scales and offsets the whole pose.

3. Verify mapping in the Retargeter

Open the IK Retargeter and confirm each source chain maps to the intended target chain. A swapped or unmapped arm chain is what produces the stretching.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every Unreal Engine error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.