What was happed is that someone killed your thralls using an exploit, probally the zath’s orb exploit that is the easest to do even. It show killed by a thief on log. Even before the new purge mob thief. There are another one that shows on log that your thrall was killed by spwaned effect. I not certainlly about this one but seen that are something related with the thrall position is they are blocking a player spwan point they die if the player logs on. But i just heard about it. I was victim of the both methods.