Lichess buggy forced mate evaluation

After rook takes queen it says #12, but after black knight recaptures it goes to +14.5. What??? Forced mate is supposed to be forced, none of opponent's moves should be able shake it off, and yet it does here, according to lichess.

Yeah, you're correct

#1 but if u give it some time it will eventually say #14 after Qxe7

#1
That is a super shock!!!!!!!!!!!!!!!!!!!!!
even i checked it its true.

yes it true programmers need to fix also the mate problems are too hard to solve

It shows mate in 12 according to best moves but @tzar_bomba don't played that move so then it is showing +14 or 15.

17.Qxe7 Be6 18.Qf8+ Bg8 19.Bc4 Nf7 20.Qxa8 g6 21.Bxf7 Kg7 22.Qxg8+ Kf6 23.Ne4+ Kf5 24.Qe8 Be3 25.Rf1+ Bf2 26.Rxf2+ Kg4 27.Qe6+ Kh5 28.Qh3#

@DJdatadriven This was the mating line ... He should play Qxe7 instead of giving Qf8+ check....

Another reason why this phenomenon might occur is that analysis is carried out back-to-front, that is: positions that occur later in the game are analysed earlier. This means that the engine can use the analysis conducted on the position after 16. .. Nxd8 when analysing the position after after 16. Rxd8+. Since 16. .. Nxd8 is clearly the only move, this effectively means that it is analysing the same position twice in a row, but it can use the knowledge it has built up the first time when looking at it for the second time. Therefore, it makes sense that the engine has not found the mate yet the first time, but it does see it the second time. Again, as @DJdatadriven pointed out: not a bug, but an inevitable consequence of finite analysis time.