My engine finds a move, but Arena plays something else...???

[JBNielsen]

[d]5k2/2P5/5K2/8/5p2/2r5/6RP/8 b - - 0 56

My engine wants to play c3c7, but Arena plays -,Rg3???

I have seen this quite often.
And mostly it plays a move my engine has never considered the best move.

What happens?


56.Kxf6
(e6f6 34 1/27 happens= M1.....78.......... easyfac=0.81 mat=1/10 sel=4,6 hash=78 hashHit4ply=447/64<score>/33<sw10> score: 34 n=1218036 time=2.93 N/S=415712 mainline=) +0.34/9 5
56...Rg3
(c3c7 -41 searched to move:10/19 Extended search at move 10! happens= L.2.4Q.78....3..... easyfac=1.86 mat=0/10 sel=4,6 hash=78 hashHit4ply=219/0<score>/87<sw10> score: 41 n=1859530 time=3.08 N/S=603744) -0.41/9 3
57.c8=Q#
(c7c8Q 29999 1/23 happens= M1.....78.......... easyfac=0.50 mat=2/10 sel=4,6 hash=78 hashHit4ply=0/0<score>/0<sw10> mate in 1 n=111 time=0.00 mainline=wrong mainline-move: 83 116 ) +M0/2 0
1-0

[abulmo2]

[d]5k2/2P5/5K2/8/5p2/2r5/6RP/8 b - - 0 56

My engine wants to play c3c7, but Arena plays -,Rg3???

I have seen this quite often.
And mostly it plays a move my engine has never considered the best move.

What happens?


56.Kxf6
(e6f6 34 1/27 happens= M1.....78.......... easyfac=0.81 mat=1/10 sel=4,6 hash=78 hashHit4ply=447/64<score>/33<sw10> score: 34 n=1218036 time=2.93 N/S=415712 mainline=) +0.34/9 5
56...Rg3
(c3c7 -41 searched to move:10/19 Extended search at move 10! happens= L.2.4Q.78....3..... easyfac=1.86 mat=0/10 sel=4,6 hash=78 hashHit4ply=219/0<score>/87<sw10> score: 41 n=1859530 time=3.08 N/S=603744) -0.41/9 3
57.c8=Q#
(c7c8Q 29999 1/23 happens= M1.....78.......... easyfac=0.50 mat=2/10 sel=4,6 hash=78 hashHit4ply=0/0<score>/0<sw10> mate in 1 n=111 time=0.00 mainline=wrong mainline-move: 83 116 ) +M0/2 0
1-0

You should keep a log file with the communication between your engine and Arena. To me, it seems that c3c7 is from the pv of your engine's search and Rg3 is the bestmove sent to Arena. A bug in your program may explain the mismatch between the bestmove of the pv searched and the bestmove sent to Arena. To be sure you need to log the data that your program sends to Arena.