Is this game normal (starting from move 17) ?

[MahmoudUthman]

This is a game between two versions of my engine , one with only PV-Search (+Qsearch) and the other is exactly the same + Null Move Pruning :
[pgn]
[Event "SFVSEN"]
[Site "DESKTOP-9IAP23G"]
[Date "2017.01.22"]
[Round "4"]
[White "+NullMove"]
[Black "original"]
[Result "1/2-1/2"]
[BlackElo "2000"]
[ECO "B00"]
[Opening "Nimzowitsch Defence"]
[Time "08:29:34"]
[Variation "2.Nc3 e6"]
[WhiteElo "2200"]
[TimeControl "60"]
[Termination "normal"]
[PlyCount "94"]
[WhiteType "program"]
[BlackType "program"]

1. Nc3 {(Nb1-c3) +0.57/9 0} e6 {(e7-e6) -0.57/8 1} 2. e4 {(e2-e4) +0.11/8
0} Nc6 {(Nb8-c6) -0.11/7 0} 3. Nf3 {(Ng1-f3) +0.10/8 0} Bb4 {(Bf8-b4)
-0.51/8 4} 4. a3 {(a2-a3) +0.77/9 1} Bxc3 {(Bb4xc3) -0.77/8 3} 5. dxc3
{(d2xc3) +0.70/9 2} d6 {(d7-d6) -0.55/7 0} 6. Bb5 {(Bf1-b5) +0.52/8 1} e5
{(e6-e5) -0.52/7 1} 7. Bg5 {(Bc1-g5) +0.54/7 0} Nf6 {(Ng8-f6) -0.34/8 2} 8.
O-O {(O-O) +0.34/7 0} h6 {(h7-h6) -0.14/7 0} 9. Bxf6 {(Bg5xf6) +0.06/8 1}
Qxf6 {(Qd8xf6) -0.07/8 1} 10. Qd5 {(Qd1-d5) +0.07/7 0} Bd7 {(Bc8-d7)
+0.08/7 0} 11. Rfd1 {(Rf1-d1) +0.01/7 0} O-O {(O-O) +0.16/7 1} 12. Bc4
{(Bb5-c4) -0.08/7 0} a6 {(a7-a6) +0.22/7 2} 13. Qd3 {(Qd5-d3) -0.12/7 1}
Rfe8 {(Rf8-e8) +0.12/6 0} 14. h3 {(h2-h3) -0.12/7 0} Nd8 {(Nc6-d8) +0.14/6
0} 15. Nh2 {(Nf3-h2) -0.17/7 1} Qg6 {(Qf6-g6) +0.19/6 0} 16. Nf3 {(Nh2-f3)
-0.05/7 0} Ne6 {(Nd8-e6) +0.43/7 1} 17. Nxe5 {(Nf3xe5) -0.21/8 1} dxe5
{(d6xe5) +0.21/7 0} 18. Qxd7 {(Qd3xd7) -0.58/8 1} Rad8 {(Ra8-d8) +0.58/7 0}
19. Bxe6 {(Bc4xe6) -0.35/9 1} Rxd7 {(Rd8xd7) +0.35/8 0} 20. Bxd7 {(Be6xd7)
-0.40/9 1} Ra8 {(Re8-a8) +0.40/8 0} 21. Bf5 {(Bd7-f5) -0.46/9 1} Qf6
{(Qg6-f6) +0.46/8 1} 22. Bg4 {(Bf5-g4) -0.55/8 1} Qc6 {(Qf6-c6) +0.55/7 0}
23. Bf3 {(Bg4-f3) -0.55/8 1} Re8 {(Ra8-e8) +0.55/7 0} 24. Rd5 {(Rd1-d5)
-0.36/9 2} Qb6 {(Qc6-b6) +0.47/7 0} 25. b3 {(b2-b3) -0.35/9 1} g6 {(g7-g6)
+0.38/7 0} 26. c4 {(c3-c4) -0.40/8 0} h5 {(h6-h5) +0.40/7 0} 27. Rad1
{(Ra1-d1) -0.35/8 0} Qc6 {(Qb6-c6) +0.35/7 0} 28. a4 {(a3-a4) -0.29/8 0}
Kf8 {(Kg8-f8) +0.31/7 0} 29. a5 {(a4-a5) -0.29/8 0} Kg8 {(Kf8-g8) +0.14/8
1} 30. Be2 {(Bf3-e2) -0.24/8 0} Kg7 {(Kg8-g7) +0.24/7 0} 31. c5 {(c4-c5)
-0.18/8 0} Rf8 {(Re8-f8) +0.18/7 1} 32. Bc4 {(Be2-c4) 0.00/7 0} Qf6
{(Qc6-f6) 0.00/7 0} 33. Rd7 {(Rd5-d7) +0.06/8 0} Qc6 {(Qf6-c6) -0.06/7 0}
34. R1d5 {(Rd1-d5) +0.20/8 0} Kh7 {(Kg7-h7) -0.16/7 0} 35. Re7 {(Rd7-e7)
+0.40/8 0} Kg7 {(Kh7-g7) -0.37/7 0} 36. c3 {(c2-c3) +0.59/7 0} Kh6
{(Kg7-h6) -0.36/7 0} 37. b4 {(b3-b4) +0.41/8 0} f6 {(f7-f6) -0.41/7 0} 38.
f3 {(f2-f3) +0.59/8 0} Rh8 {(Rf8-h8) -0.59/7 0} 39. Rdd7 {(Rd5-d7) +0.78/7
0} Qa4 {(Qc6-a4) -0.76/8 0} 40. Rxc7 {(Rd7xc7) +1.17/8 0} Qa1+ {(Qa4-a1+)
-1.17/7 0} 41. Bf1 {(Bc4-f1) 0.00/9 0} Qxc3 {(Qa1xc3) 0.00/7 0} 42. Rxb7
{(Rc7xb7) 0.00/8 0} Qe3+ {(Qc3-e3+) 0.00/7 0} 43. Kh2 {(Kg1-h2) 0.00/9 0}
Qf4+ {(Qe3-f4+) 0.00/7 0} 44. Kh1 {(Kh2-h1) 0.00/9 0} Qc1 {(Qf4-c1) 0.00/7
0} 45. Kg1 {(Kh1-g1) 0.00/8 0} Qe3+ {(Qc1-e3+) 0.00/7 0} 46. Kh1 {(Kg1-h1)
0.00/9 0} Qc1 {(Qe3-c1) 0.00/7 0} 47. Kg1 {(Kh1-g1) 0.00/11 0} Qe3+
{(Qc1-e3+) 0.00/7 0 3-fold repetition} 1/2-1/2
[/pgn]
starting at move 17 to move 19 seems strange to me ?

[PK]

Sequence looks strange to human eyes, but is not indicative of an error. Rook, bishop and pawn are only marginally worse than a queen and other evaluation factors might compensate for that.

There is also a possibility that Your engine wanted to play 19.Qa4, and evaluated position after that move statically. From the chess point of view this is an error, because the move fails after 19...b5. From te programming point of view, the fix is to search deeper - so again, probably not a programming error.