Why is 36.Nf4+ a blunder?

Just looking through one of my opponent’s games and got curious.



It says it loses the forced checkmate sequence with Bd7+, but after moving Nf6 or Bb8 it says it’s a mate in five, same amount of moves.

Probably the server analysis just didn't look deep enough to the forced mate there as well.

Kdyby táhl bílý králem na g5, tak by to byl po tahu černé dámy na h5 mat.

Quite strange, as even at depth 14 it shows the mate sequence...