I would log the tweentime and x,y position of the sprites, as I think the tween must be responsible for that behaviour.
Sync() is like a tank, no matter what it will be executed each loop if not told otherwise.
There is aswell no hidden buffer that may save any rendering information for more than one frame (the swap buffer can't do such jumps)
I suspect a float value going above a certain treshhold like
stuffset(v#) // where v# can't be > 1.0
if v#>1.0 then stuffend()
but v# can't be more than 1.0 or everything will be moved to 0.0 tween
Such a construction is able to trigger such a rendering error.