I can think of two possibilities (but I guess a more experienced player will correct/add me)
in the past it was possible to capture AC thanks to expoit , maybe she is one of them in the service of another player - but I guess that shouldn’t be a problem on PVE-C should it , only on PVP ?
recently we couldn’t find the scorpion queen that is at the end of the silver mine (we went there because of a BP challenge) , she wasn’t where she was supposed to be and didn’t respawn even after 30 minutes , I finally found her by chance outside the dungeon near Serpentmeru , maybe it’s a similar case and AC took a trip…
There is an exploit to knock the arena champion. Then the player drags the arena champion to your base and within a couple of minutes she wakes up like any regular NPC being kocked out. At that time, she will agrro on nearby thralls and kills them all.
This exploit is old and never got fixed.
Keep your thralls indoors.
My train of thought: Is it possible to drag Arena Champion to the end of The Wine Cellar and see if Thag, or even one single Wight would be foolish enough to attack her?