My door when in the open position sags in the middle at the second to the bottom panel (all the way across like a V). When I press close the door panel SNAPS into place when it is about to go down from the up position. To close the door I have to push up on the panel at the middle so it is not saging. I looked and tightened every bolt and still could not get the door to operate properly. What do you think is wrong with it?