optimum chess endgame with D=3 pieces doesn't give an exact moves_to_mate variable

[max22]

I have just upgraded my code for computing completely optimally for both players a chess endgame as given here:
https://pastebin.com/jQ090L01 but it gives to me 2 plies to checkmate White instead of correct 4 plies according to StockFish.

Can someone give me a hint how to fix this and where is the source of the problem?

There are no errors and the code is provided. I do not follow what do you mean.