We were killed, because I don't know how we were supposed to live against that :P
Also, I was not able to reproduce the issue, we are not sure how it happened. My best guess is that it is related to skipping the cutscene before the engagement because the screen flashed oddly after canceling it.
You can see in the video there are clearly two Izual bosses on screen at once. One in the upper right-hand corner and one in the center of the screen next to the other two angelic hammer mobs.
The third attempt was only one boss, and we succeeded.