Michael Arnold said:

I sent an attack to 1686;-295 and it just disappeared and I lost all of the troops that were sent. I have no report about the attack. The attack never reached the city. I sent out another attack at the same time to a different city and it reached the city and came back with no problems. 

The most likely answer is that your troops reinforced the city and did not attack

Check your garrison - the troops are probably sitting at 1686:-295

If not then check your healer/infirmary for dead troops