That bolt in the picture is not supposed to have any washers. It is simply a jam bolt to help keep the hitch head in position. The washers should be on a pin located above that bolt and between the hitch head and the shank. They determine the amount of tilt on the head.
See #26,27 and #19 in the following parts breakdown.
Equal-i-zer parts breakdownIf that bolt pictured is not tightened up against the shank then the whole head could possibly shift back and forth and may be what you were experiencing, especially if the two large bolts holding the hitch head onto the shank were not torqued to specs. I believe the torque on those two bolts is in the neighborhood of 350 -450 lbs.
Barney