Broken cable or spring drops one side
When a lift cable snaps or a torsion spring fails, one edge of the door falls while the other stays supported. Rollers jump the track flange, panels rack, and the opener may keep trying to lift a twisted door. Realignment alone is not enough — the failed counterbalance part must be replaced first so the door can sit level again.
Look for: loud bang, sudden tilt, cable hanging loose