Incorrect deformation when copying bones

I have a SkinnedMesh that is in A-pose and I’m trying to change it to a custom-pose using an armature exported from Blender.

I am able to get to the correct pose but am seeing strange deformation around wrists.
Screenshot from 2021-11-23 12-25-03

Any idea how to solve this?

Current code:

// node is my SkinnedMesh

_.each(customBones, customBone => {

    let bone = node.skeleton.getBoneByName(;
    if(bone) {