When I got to the point of fighting ISIC’s last form, he throwed me all the way up to the top of his chamber and followed me there. Then I fell all the way down back in the chamber but ISIC was stuck in the entrance hole and never came back.
Since I was playing solo with Rath it was impossible for me to reach him and my health regen was greater that his weird lightning field attack.
I had to quit the game and lose all the progress done in that cession.