That was my thought too. Does the engine know that the other player is forbidden to play the top engine move on the next turn? Then you can't just do something like c3 Nf6 Qa4 e5 Qe4!? to hang the queen in the center, knowing that Nxe4 is prohibited, because the strongest move for white if Nxe4 is prohibited would have been Qe4!

Any move the human chess engine makes would be losing by definition if it is also used as the bench mark.

Therefor, such an engine can only hang in computation - being unable to produce a top move because if it were to make a suggestion then the actual best move changes to avoid it. Since the engine is unable to produce a move - there is no top engine move which makes every move legal.

A normal game of chess is played while the engine locks up on the sideline

You forgot that the engine user may cheat and even if they declare the engine there's no real way to detect if they're truthful and not using a certain of the engine tuned for Human Chess specifically.