Can you help us get our robot unstuck?

[thinker&planner]

It seems like there should be a "sweet spot" where it should release. You jut have to keep testing to find it, but you might consider opening up the grabber/hook part so that it is a little looser. This could be dangerous but might be enough to free it.
An alternative to the piston (If I were on your team, I would rather not add pneumatics for just one thing if you can do it with a motor) would be using a smaller motor (BAG or Bane Bots w/gearbox) and a cam/eccentric wheel to push away from the pyramid corner as you lift the bottom claw/gripper.

Regardless of how you end up doing it, you should definitely program the climb to be autonomous. If you find a sweet spot, it would be completely necessary to automise the climb.