Recently the door would occasionally reverse when closing. Yesterday I
couldn't make it close by pulling on it (figured the tension might be
wrong). Disconnect and it would almost fall shut so no friction
problem. Been awhile so I cleaned the IR sender/sensor. Closed. Aha!
fixed it...nope. Did the same this morning. Tested the indicator
light - yep, it is seeing the sendor. Cleaned again, door still won't
close. Was just heading for the house when I noticed this little bitty
sprig of cheatgrass with a flimsy head on it leaning in the door.
Picked it and door fixed! That explained why it was intermittent -
depended on how the breeze was blowing. It may have degraded the
signal by about 50% which was apparently enough.

Harry K