I followed your advice Admin Manijak and waited for the score to settle for 40 secs, my score went from 35095 to 35220, then after waiting for the correct cube to appear I opened that mail and got the incorrect cube again.
It happens,bcs mission war channel is saving score in sequence of time.
when mission war is ended, yours score is saved from last update sequence of time.
what you see in yours window is probably score you did, but server dont see that.
best way is to try not to do any score last 40-60 sec of mission war. and reward will be correct.