Welding doesnt work on Character RightHand if not default roblox character. Help?

So I was trying to Weld A Scythe to My Characters Right Hand with a weld constraint using a default blocky r15 body. Worked fine. But then I noticed that if the Right Hand is a different package like the Zombie body, It Doesnt work at all. Heres the Code:

    local DefaultScythe = game.ReplicatedStorage.Assets.Weapons.Handle:Clone()
    DefaultScythe.Parent = Character

    local WeldConstraint = Instance.new("WeldConstraint", Character.RightHand)
    WeldConstraint.Part0 = Character.RightHand
    WeldConstraint.Part1 = DefaultScythe

    DefaultScythe.CFrame = Character.RightHand.CFrame*CFrame.new(0, -1, -1)*CFrame.Angles(0, math.rad(90), math.rad(-90))