even in same animation, different bone length and different skin and mesh will cause totally different cases.
Firstly, you need to check your two mesh start post, just like, same T Pose or A Pose, different start pose will cause different result, SO you need to make sure that your two different mesh has same start pose, Secondly, there will cause some trouble if your two bone length is different ,so you need to search some solution to solve the name like"fix animation of different bone length of IKRetarget "somehow.