Oh man, I just got stuck.
It was in the Trick House, challenge #4 I think it was (the first time you use Strength). I was so ticked off I forgot to save a screenshot.
Near the end, just before the last trainer, you have to push 2 boulders on to the slippery floor against a wall so you can go left/right. While pushing one, I accidentally pushed it over to the left past the gap, blocking my path, and the floor wouldn't let me go down. Escape Ropes don't work in there.
All I lost was my progress through Cloudain Gym, but still.....