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).
There’s a decent amount of force on them so unless your caps are a really good fit I guess there’ll inevitably be some creep. I’m not sure I’ve ever taken and old cable/cap off and not seen at least a hint of it
….so that there is a bit of exposed inner metal wire casing protruding beyond the plastic sheath ?
My 6 month old Anthem was shifting a bit poorly last few rides, needing regular barrel adjustment so reckoned cables would be a good start. Half an hour faff with internal routing later and new outer and inner sorted. The factory outer was Jagwire and both end had pulled through by around 5mm. Why does that happen, more often with factory cables.. ?
New SP41 and Xtr inners fitted and it’s shifting properly again.