Dead arena in Desert Vault, cannot progress

(See diagnostic screenshot at the button)
There is nothing alive in here but me, i have been all over this huge room 5 times and checked every corner. The button is not lighting up. I pressed it once so far; the first round doesn't seem to know it's over. After 20 minutes, about to bail on vault. Standing in various places and listening, I hear no bound or other hostile noises - nothing in the walls, nothing i can hear anywhere. It just seems to have failed to detect the deaths of all hostiles from the previous round.

....while i was filling out this report and putting all this together, a Bound ran up and attacked me. After killing it, the button became active. Wherever it was, it look literally 20 minutes to find me.....