I was attempting to reuse a door when I installed my pocket door for my bathroom. As I installed the handle, I noticed the door is rubbing in the middle of the jamb. Where my guides are at the bottom, there is ample space, same as the top, middle, definitely leaning towards one side more than the other. Will/should I just replace the door?
Use a straight edge, your eye, or a string to see what is warped. If the door is warped, then fine, replace it. But I doubt that the door is warped. It is much more likely that the wall is warped.
Unlike the door which has this and that engineered into it to keep it flat, there is nothing in a 2x4 to keep in flat. All lumber is crooked and most likely the wall builder forgot to crown the 2x4s away from the door so that the gap in the middle would be larger than the gap on the top and the bottom.
Do check just in case it is the door that is crooked. Also the hangers on the door usually allow to horizontal positioning. Play with that to send the door toward one side and see if you can stop it from rubbing.
Otherwise.... Oops. Time to cut the 2x4 out of the wall, flip it around, and reinstall.