Teleporting the root body doesn't imply resetting the articulation pose actually, all it does is to move the root, and make all the children follow on with the offset. Unfortunately, that creates some residual velocities in the spherical joints code that PhysX can't really deal with. Until we have a proper fix from Nvidia, we recommend to obtain pose somewhere during the init sequence (with articulationBody.GetJointPositions), and then immediately apply this pose right after teleportation. This will have the effect of resetting agent to initial state safely & reliably well.