120hz changing to 60hz

As the title states, my game(Xbox Series X, NIR, 67%) will refuse to allow me to run in 120hz mode now, with the game disabling both 40hz and 120hz(I have the ASUS ROG SWIFT PG27AQDP so it’s capable), since reaching Act 3. I have also noticed a lot more screen tearing and flickering in this Act. I don’t know what happened or why, but it doesn’t want to work.