I began a second max surge immediately after the first (back to back) however after the first wave of the 2nd one the thralls stopped dropping.
Looked everywhere carefully, rode a ring at different distances around the shrine many times as well as re-rendering the area then relogging. Did this for 15 minutes.
There was one other player hanging around, casually hoping to nick a Thrall whom I told to get lost, who then apologized and seemingly disappeared. I don’t think it’s possible for other players to lead a Thrall away and keep it engaged somehow so the drops stop /paranoia.
I had that happened to me the other night, end of 3rd round, it didn’t drop for 4th, I ran all over the place looking, finally found the one darn thrall way way away from the shrine. it seemed it chased off a buffalo and was almost a block away … fish gill man to be exact. killed him but by the time I was able to get into to the last round for a sec storm started and ended my lil play time…
So yes a player or even a NPC they can chase seems pretty far and get stuck…
wish i knew that night cause it hurt to waste 20 greater for the surge and not finish it… but it was almost two block away and, wasn’t stuck in a rock or nothen it was just standing there