A Bent Track
A track out of alignment makes the door bind, which puts load into everything else, which is how one small problem becomes several.
Short answer
The usual causes are a vehicle impact, loose mounting fasteners letting the track move, a door that came off the track, and settlement of the jamb the track is fixed to. A minor bend can sometimes be straightened; a kinked or creased section is replaced, because a door running over a crease wears rollers fast.
What causes it
A vehicle reversing into the track or the door, which is the most common cause by a wide margin.
Loose mounting fasteners, which let the track drift out of alignment slowly.
A door that came off the track, which bends the track on the way.
Settlement or movement of the jamb or the header the track is fixed to.
The horizontal track sagging because the rear hanger has come loose or was never properly fixed.
And corrosion at the bottom of the vertical track, which weakens it and lets it deform.
What a bent track does
The door binds at that point, so the opener has to force through it. That wears the roller, scores the track, strains the hinge and section, and masks the real problem behind an increased opener force setting. A bend that is left alone becomes a roller failure, then a hinge failure, then a door off the track.
Straighten or replace
A gentle bow in otherwise sound track can sometimes be corrected by loosening the mounts and realigning.
A kink or a crease is replaced, because the deformation remains even after it looks straight and the rollers find it every pass.
A corroded section is replaced.
Track alignment is a measured job — the vertical sections plumb, the correct spacing to the door, the horizontal sections level and parallel.
The rear hangers should be properly fixed to structure rather than to drywall or a single fastener.
And after any track work the door should be cycled slowly and watched, then balanced and the opener reset.
Preventing it
Fit bollards or a wheel stop where the garage layout invites a reversing impact.
Tighten the track fasteners at the annual service, which is the main preventive measure.
Keep the opener force set correctly rather than turned up to force through a binding point.
Deal with a binding door when it starts rather than when it stops.
Keep the threshold clear so the door is not closing onto obstructions.
And watch the door operate occasionally rather than driving away, because a track problem is visible before it is audible.
Common questions
Can a bent track be straightened?
A gentle bow sometimes. A kink or crease is replaced.
What does a bent track cause?
Binding, which wears rollers and hinges and eventually puts the door off the track.
How do I prevent it?
Tighten the fasteners annually, keep the opener force correct, and fit a wheel stop if the layout invites an impact.