I had 3 tribesmen against 1 deer. When I ordered one of them to attack, the order was accepted, but the attack itself didn't happen. I couldn't reassign the order, all other actions seemed to have been queued after the attack which didn't happen. The battle couldn't progress because of this, so I had to load my save file.

It happened 2 times to me.

Save Files.zip

A have the same issue right now, here are the two save files, one as autosave and the other one as stuck right now.
I started a battle with 2 scouts vs a mammoth, and didn't see him at first.
Had to move one down and then attack him downhill, then tried the other one and he just moved without attacking.
I have save this file, and loaded it up again and then the mammoth moved so if you experience this bug just save and load.