Possibility of a rear steer cylinder bypassing internally past the piston. Or by passing in the 6 port steering change over valve (valve locks fluid flow to rear steer when in side mode). But since its intermittent I would recommend looking into and installing the rear steer cylinder check valve kit (CPHY0455) if you have a rear steer cylinder p# CMR00024 as this kit was made to prevent rear steer cylinder from creeping.