Animation Retargetting Error (Right Arm Only)

Hi everyone,

i was hoping someone could assist me with a bug i am having when re-targeting the standard character animations over to a custom mesh.

all the animations seem to work fine except for the right arm, from looking at the animations, it seems that from the elbow down, the skeleton is not binding to the mesh, so the arm is stiff while the bones are still moving.

does anyone know what the cause of this could be ? is it a problem with the re-target or could it be the actual mesh i modeled. also, the skeleton i used is the UE4 skeleton so the naming of all bones is identical.

Translation Re-target Information:

root - Animation Scaled
pelvis - Animation
all other bones - Skeleton