Hill giant stuck after zombie random event

Hi there,

I was ranging hill giants from the safespot with 3 giants, when suddenly the zombie random event triggerd.
He attacked me, so I ran a little bit away and came back. He stood there in front of the hill giant, so I attacked the hill giant in a way that the zombie is in front of him, basically using the zombie as a safe spot.
Then I accidentally attacked the zombie (the hill giant was still alive), ran away again, but this time far enough to get agro’d again, and ran back to the safe spot. The zombie was gone.

But then I attacked the same hill giant that I previously attacked, from the same safe spot, but this time it was unable to move. It wanted to move, because it was facing me, but it was stuck there, as if the ghost of the zombie was still present on the same spot:

I could kill him from this distance. Is this a bug?