When fighting a deer, it split into two. I was able to attack both at first and kill one. However, after I attacked one of them for the first time, it seemed that I couldn't attack it again. It said that the path was unavailable or something like that (although it seemed perfectly open), even though I tried to hit it with an archer and melee units. Ultimately, I had to wait for it to kill itself when it attacked me in order to finish the combat.

Did it really split or did a aecond deer enter the battlefield, which is already possible.

That's a good point. I wish I had remembered to take a screenshot. I want to say the deer's army split up just like the player's army can, but it's possible that there was another deer in range that was also engaged. I'm not too sure about the limitations and rules of Humankind's combat yet. Is there a reason you can think of why I wasn't able to attack correctly?

That seems to be a bug. I haven't fought in open dev and never experienced a similar situation.