Did you check to make sure that all the properties were cloned? In this situation you might want to check that the JointInstance | Roblox Creator Documentation is being set. Also, you should should parent the clone after setting its properties. This not only provides a performance improvement, but I’ve noticed in several post that this is usually the issue. So you would instead use:
local HRP = Character.HumanoidRootPart
local LeftHip = Character.Torso["Right Hip"]:Clone()
local RightHip = Character.Torso["Left Hip"]:Clone()
LeftHip.Part0 = HRP
RightHip.Part0 = HRP
LeftHip.Parent = HRP
RightHip.Parent = HRP
Another thing you should know, when referencing an object multiple times, in this case Character.HumanoidRootPart, you should store that object in a variable instead because it will improve performance.
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I just typed that whole response and then looked at the source you provided. Oh well. In the solution to the referenced post it says:
In other words, you need to create a new animation for the legs and replace the default animation. You can check out these links for guidance