In this top image the circled unit is in full retreat just spinning in circles, I can sort of understand it because there are still lots of units in battle around it.
Here a minute later with most my units chasing the sole retreating unit it is still spinning in the same location.
I have had one of my units do this in the past, be stuck between armies and an obstacle and just spin in circles. Mine came out of its retreat and then I was able to give it further orders. This one kept spinning so I took the screen shots and circled it. Hope these help you figure out why they can't pick a direction and go. But they do look like pretty ballerinas doing their spins. If it matters both incidents this one and when mine spun were in nightmare solos today.