Vancouver sits in a mild band with some freeze, not the deep-freeze cycles that crack concrete apart, but enough to matter. A slab that holds steady most of the year still shifts a few thousandths when temperatures dip below freezing overnight, and that's enough to nudge a track bracket that's bolted into jamb framing rather than poured concrete. Add in the wet months, and wood jambs swell slightly, which changes the angle the vertical track sits at relative to the door panel. Neither movement is dramatic on its own. The problem is that it happens every year, in both directions, and track hardware doesn't flex back to center on its own. Over enough cycles the track walks out of plumb by a degree or two, which doesn't sound like much until a roller starts riding the edge of the rail instead of the center, and that's when a door jumps track on a cold morning instead of running smooth. We don't get the frost-heave damage that cracks foundations, but we do get this slower, quieter version of the same thing.