I have a sphere that isn’t anchored but it’s massless, and it’s welded with an NPC which is also not anchored but it’s massless and without collision, the current problem is that for me the sphere is not rolling, like if it would be too heavy to roll, here is the model:
PhysicsSphereIssue - rbxm file (6.5 KB) Feel free to use it in your games :)_
Sometimes it stops randomly when it rolls, and for any reason, it returns to it’s original rotation, it’s expected to roll as a normal sphere, thanks for reading 
I believe you need to set the NPC humanoid’s state to “Physics” for the humanoid to not attempt to stay upright and resist movement.
More info: HumanoidStateType | Documentation - Roblox Creator Hub