LiftMaster Elite 3585S - Door opens/closes only upto/from 9 inches

Chamberlain LiftMaster Elite Series - Model 3585S. Made in 2009.
The door behaviour is same whether using remote or wall mount button. works fine manually.
Door opens only about 9 inches then keeps making sound as if something is stuck, motor keeps running, until i press the button again. 
If the cord is released, the engaging part goes all the way up and down.
if the door is more than 9 inches above the ground, cord engaged and then try to close then it does not move at all and makes the same stuck sound. 
Closing works only from 9 inches to the ground. 
I don't see any obstruction in the rails, wheels, cables etc. Sensor is steady green, clean and not obstructed and not loose. 
Spring doesn't look like broken or lost tension. 
if left open half way, it stays there, so spring/coil seems fine.
What else can i check/try?
Please see attached video.

Thanks in advance