Following this video, Is there a way to release or counter Cutting Armbar from Shoulder Crunch?
From experience, I can tell you that if the opponent has good distance control - as they should have via their feet at your hips - and do an actual shoulder crunch it is hard to impossible to escape it.
That being said, I stumbled over this video. There, the instructor suggests to bypass the leg on the side where your shoulder is held and try to fall to the side so that your forearm ends up between the ground and the opponent's neck.
Generally, I'd say that the key is to get weight on that arm and the guy is correct. Otherwise, you would have to rely on severe technical mistakes of the opponent.