When going into Mordremoth's mind, I selected Canach to go in with me. This leads to fighting the vision of Canach. In short, this fight is bugged. After the vision of Canach's health lowers to the threshold where he starts throwing grenades, the real Canach goes into his mode of putting up the shield to block/reflect the grenades. This part is fine, but then what happens is Canach will never go back to fighting and gets stuck running to different spots and shielding. The sequence about opening & widening the rift to defeat the Vision of Canach never prompts. In the attached screenshot I managed to defeat the Vision of Canach by reducing his health to zero and he disappears, with the rift sequence never happening. Meanwhile Canach is still shielding and the story never progresses.Here's a screenshot showing Canach shielding, the story still says Defeat the vision of Canach and there is no vision of Canach in sight. Imgur link