Could be the hose - sometimes the inside of a hose will collapse uner one direction of flow but nor another. The raise flow direction is also under considerable pressure - more so than the lower flow direction.
Could also be a valve problem in the hydraulics/hydraulic pump, including trash, a bit of hose, or a stuck valve. If one cylinder works finae and the other one diesn't I'd suspect a hose or hose attachment point problem, though.
