Thirty-year roller deterioration
Thirty-plus years later, a big share of that original hardware has never been swapped out. Nobody replaces a roller that still spins. That's exactly the hardware that walks a door off its track. The nylon or composite rollers from that era wear a groove into themselves over time, and once a roller gets narrow enough, it can pop clean out of the track on a cold morning when the steel has contracted slightly and the tolerances tighten up.