You can get forward by making all your characters give the source away, otherwise it bugs. Other way is to manually kill dallis to 20% hp when the bug occurs and it makes the story go on. Prepare for the most impossible fight in your life though.
You`re exaggerating it too much, not impossible at all, kill braccus Rex and it`ll be end.
Most irritating thing was levers before final meeting with Lucian. I uttered thousands of damns at that moment.