Most of the tract homes through Chino Hills were built around 1990, and by now the original steel rollers on those doors have put in three decades of daily cycles. Steel rollers wear at the wheel and at the stem, and once there's enough play, the roller can walk sideways out of the track instead of running straight through it - that's the moment the door goes visibly crooked or jams partway up.
The area doesn't carry the freeze-thaw stress that cracks track brackets in colder climates, so most of what we find here is straightforward wear rather than weather damage: a stretched track gap, a loosened roller bracket, or a cable that's frayed enough to jump its drum under load. It's mechanical fatigue on hardware that's simply done its time, not a symptom of anything dramatic happening to the house.
A door that only comes off track on one side, near the bottom, is almost always the bottom bracket or the roller closest to it - check there first before assuming the whole track needs replacing.