nothing special about these, they lower using gravity, no power assist.
do you have a load on it? or does it just do this with no load?
i would check the mast channels and rollers but i'd bet the packing is just tight and the cylinders are getting stuck.
bet if you get some weight on it it will come down.
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.