Whoever invented pocket doors must have been laughing to himself when he considered the poor slob who has to repair them.
My 1967 house has three pocket doors and I have had to fix all three in the eight years I've lived here. It's always the rear roller that either falls off the track or the adjustment gets out of whack and the inside part of the door drags on the floor. The one I have looks like this:
I spent the weekend tearing off the moulding around one of the doors just to get to the rear roller. This time I modified the top frame so I wouldn't have to take the entire moulding around the door off just to get the top one off. It's finally all back together and the door rides correctly. I'm hoping this is the last time for a while.