I got the same issue, after interacting with the Wellspring Dallis and Vredeman show up and nothing happen.
The solution i found was to kill all the other godwoken (ctrl + click on them) just before entering the arena, then you talk to the automaton en enter the arena just with your team. Interacting with the Wellspring then made Dallis and Vredeman appears and a dialogue with Alexandar, then after an autosave, my game crashed, but i was able to load the autosave and continue.
