How do I fix this strange animation bug?

[Roma-britania]

Ok, so I am attempting to create a new armour set using different pieces of pre existing meshes provided by the game. one of these pieces is the Khuzait_leather_Armor_b, whichI was using the arms and shoulders for, which I encounter this strange animation bug that seem to appear once you reimport the model mesh back into the game. once you apply a animation to the armour, the two shoulder leather guards suddenly become wonky and Frey at the end.

Has anyone else encountered a problem like this before? Any help would be fantastic

 

[genrev0914]

you might want to disable "add leaf bone" on blender when exporting your mesh.