Spoiler warning, struck through to prevent accidental reading, hopefully: the problem was that it wasn't yet clear the implicit versus explicit operations had different priorities. But that's a complex lesson to learn in such a convoluted puzzle, in my opinion. I think (at least) an extra puzzle to reinforce this would have been great! Especially since the "order of operations" was a handful of puzzles in the past and thus no longer fresh in my mind.
There were also lessons about the yin-yang sign itself in the mix. Again, I think it was too much.