Hi,
Without access to the project itself it's hard to tell but my gut feeling is one or both of these possible routes:
-- you are mixing update and late update and physics right? if you use physics, you must use the right call ( likely everything on LateUpdate) to properly avoid jittering.
in this case, check out the ecosystem, I am slowly but surely making a series of "Advanced" actions that are exacty replicas of PlayMaker actions only you can choose the update call properly, and thus totally control and get rid of this kind of jittering.
-- prefer NOT to synchronize the position at all time, but instead send discrete events everytime the ball hit the wall, givine the direction it will now go, which is enough to then compute on all clients the movement of the ball after each of these events are fired. This way you completly avoid lags, and the onle point of "blurryness" in your logic is the lag of the event being sent over the network, which is dramatically less then lags that would happen on a constant stream of data.
Bye,
Jean