My garage door would occasionally not close. It would get to about one half to three quarters closed then reopen. I would have to stop it and make another run at it.
It was not the infrared sensors of the garage door.
I tried adjusting the garage door motor adjustment potentiometers according to the manual.
I had even contemplated replacing the unit, suspecting the potentiometers might be noisey.
I tried readjusting the rails of the garage door, thinking they might be out of alignment.
I contemplated adjusting the tension on the garage door springs. But fearing I would knock my jaw off, I thought better of it.
Guess what was causing it. The garage door springs were rusty. I sprayed the garage door springs with WD40 and it has not done it since. I am assuming the rust between the garage door spring's loops was causing the garage door sensor to think it hit something, and thus open again.
As I did not find any sources on the internet to share this tip, I felt it my duty to do so.
Note: Always disconnect your garage door from the chain before adjusting the chain tension. If yo do not, you might snap the drive gear off the garage door opener. Lesson learned.