Maybe it’s not a bug and something just killed your thralls.
1.You were Online or Offline this happend?
2. If you were Online, did you died and did your thrall died left on the map without leadership?
3. If your thrall died while you were Online and after you died are you shure Behaviour of this thrall wasn’t set to “Do Nothing”? If so, thrall could be killed by anything as it wouldn’t defend itself.

I had this bug recently that my thalls didn’t pull out their weapons, they were fist fighting only. Maybe it happend to your thralls as well. I didn’t report it. It’s so exhausting to report stuff.