''I wonder if it's "reversing" (Not closing on it's own) because it's binding or hitting an obsticle'' near the end of the upward portion of your track - '''check your supports, one may be lose or have dropped a bolt/nut that's in the track.''' If you have torsion springs the cable drum/pulley may bind at the end of upward travel.
There are "tensions" or adjustments that can change the amount of pressure before reversing starts.... that may have vibrated to a setting that's too quick to reverse.