Diagnosis
The force limits are set too low. The opener thinks it's hitting an obstacle. On the 8355W, there are separate 'Up' and 'Down' force adjustments.
How to Fix It
Adjust the 'Up' force. On the back of the motor unit, find the two black adjustment dials next to the learn button. Turn the 'UP' force dial (usually the left one) clockwise one notch. Test. Repeat if needed, but only small increments.
If That Didn't Work
The door springs are out of balance. Manually disconnect the opener using the red emergency release cord. Lift the door halfway. If it doesn't stay put, the springs are weak. A professional must adjust or replace them.
Heads Up
Do not over-adjust force settings. The door should reverse on a 2x4 placed on the floor. If it doesn't, the force is too high and unsafe.