When an avatar is uploaded with a non-unity scale, animations when viewed by others are shifted.
See below (Left is the avatar wearer, right is from a secondary player's perspective)
The avatar in question has a scale of ~0.454, which shifts the animation down.
If the model is scaled up (to say a scale of 1.4) then the animation is shifted up
This issue was also reproduced with another model, so it's unlikely to be a rigging issue.
The SDK 2.0 version of this avatar doesn't have the same issue. so I believe the issue to be SDK 3 exclusive