Possibly expansion of the outer wires and/or shrinkage of the outer cover.
Though decent quality ferrules reduce a lot of issues. Rubbish ones tend to split or pull away from the outer at the lever, expose the cable, then moisture gets in and I wonder if that causes expansion of the outer’s wiring. I’ve seen it worst with exposed ends and the outer wiring starts to fray and become exposed like it’s expanded outwards.
Got a pack of hard ferrules that don’t bend easily and split, and are tight fitting so don’t pull off easily and expose the cable. Though I forget what they were as was a while back and a big pack that’ll last me years. Barely use them as the cable inner and outer lasts for years too (SP41 plus any old cheap stainless steel cable).