The cause is the awning has slid a little on the roll up tube. It is causing the jam on the end frame. If the top of the arm is towards the nose of the Monty then when the awning is unrolled pull the material toward the nose of the Monty. It will realign the arm. Orv's comment to push up on the arm is correct and saves climbing on the roof. I also use the awning poll with the hook to grab the top of the arm and pull out after unrolling the awning a couple inches.
Good luck, let us know what you find and safe travels.