Check the linkages from the position control lever and .....whatever it is called, the rod that communicates back to the valve where the rocker shaft's position is.
Low fluid check first, but I was assuming that you would have already done that before posting ?
Make sure the lever is all the way down and/or the top link is in the hole that isn't affected by draft control. Draft control senses downward force on the 3ph and could cause the symptoms you describe.
Your piston seals leak. Take off the 3pt lift cover with a workshop engine lifter (if it has a cab and you've removed the floor) and you'll see the big piston underneath.
The cylinder leaks oil and the position control keeps correcting that.