Scenario 1: door goes down not all the way and comes back up.
Towards the bottom of the two vertical tracks, there are 2 separate sensors with photo eyes facing each other to maintain a beam across while the door is coming down if this beam gets interrupted for whatever reason the motor assumes there is an object in the doorway so the door goes back. Commonly this beam gets thrown out of alignment when it gets moved/pushed accidentally, this can be fixed by adjusting it finely, ie. moving it gently by hand until you get the lights the green and the orange solid and steady again, both lights must be ON must be solid and bright, no flicker or blink and that is when you know the sensors are aligned now.
Scenario 2: sensors are perfectly aligned and you are still having the same problem. As the door is coming down at a very specific spot along either vertical tracks due to a mild bump, weak structure, or just a loose jam bracket, the track gets pushed outward and throws the beam out of alignment. Framing around the door (garage structure) and all the tracks hardware needs to be checked and reinforced.