Can I unwarp sliding pocket doors so that they move freely once more?
I had the same problem, and was able to resolve the problem by counter-bending the door.  You can try it in the frame, or you can remove the door and use some wood you might have laying around.  If you do it in the frame, you won't be able to operate the door while you're working on it, and it will probably take a few days. But the idea is to stick some wood or something to make the door bow the other way.  You'll need to be creative so you don't scrape-up the door. If you can figure a way to counter-bow the door by hand, then slip the scraps of wood in there, that would be good.  Maybe put the top and bottom scraps in there, then get someone to heave on the middle section while you slipped another scrap of wood in there.  Trying it in the jamb might take longer because you can't get that much of a counter bend in it, due to the frame only being so wide.  Taking it out of the jamb might be faster, since you can get more of a counter bend, but obviously removing pocket doors can be tricky.