Aren't there situations where 2+ moves cause checkmate? Only one can be the top engine move. Or are all of those effectively impossible to reach unless your opponent helps?
> When multiple moves have the top score, they are all top moves, even if visual markers (like move arrows) suggest the engine prefers one over the other.
Since all moves that checkmate the opponent will have the same score (M1 or -M1) they'll all be illegal.