I've watched videos, searched the web & forum, and posted my question on Facebook. I've tried moving the stones into place numerically - backward & forward. I even followed the steps others used in videos precisely as they moved them, putting the stones back exactly as they were to start completely over (I think I did this at least 3 times). The thorns still stand.
I really hope I'm not obliviously missing something. Someone please just tell me the answer? I've cleared all the other stages of the event.