Example puzzle (I'm sure there are numerous that fit this bill):
[FEN "rnbq3r/pppp4/3b1pkp/5p2/2BP4/4P3/PPP2PPP/RN1QK2R w KQ - 0 1"] [Site "Earth"] [White ""] 1. Qh5+ Kxh5 2. Bf7+ Kh4 3. Nd2 Bb4 4. c3 f4 5. Nf3+ Kg4 6. e4 Bxc3+ 7. bxc3 f5 8. h3#
I've found a 8 move checkmate that takes Stockfish a depth of 36 ply to solve. Since the checkmate is only 16 ply deep in the game search tree, what specific mechanisms cause the engine to take 20 ply longer to find the solution?
I understand that the high level answer is engine selectivity. However, my understanding is that Stockfish's forward pruning tended to be pretty safe (such as null move pruning). Plus, if the solution were being forward pruned, wouldn't it keep being pruned even at later depths?
(The winning move is a check, so it shouldn't be reduced by something like late move reduction anyways.)
(Crossposted...will be sure to update if anything comes of it)