The Bowden cable is quite a convoluted affair with a centre steel wire core encapsulated within a polyethylene, (or similar plastic), all of which slides within an outer plastic/wire sheath, (from memory so I could be slightly incorrect)!
My shift was extremely tight so I removed the cable, (whilst I was stripping the interior), and noted at that the outer sheath was kinked and this was pressing on the inner core.
I was fortunate that the damaged area was right at the end, (close to the transmission lever), so I could trim it back thus removing the mechanical obstruction.
I doubt whether yours will be mechanically damaged, (if there is no history of any 'mishaps'), so lubrication may be a possible solution although not sure what lubricants are recommended for the inner cable, (as it is a plastic derivative the wrong lube may cause the inner cable to swell thus making matters worse)!