Strong lag when changing state for camera and hero

Hard to explain but easy to reproduce. I don't know the exact engine reasons that causes heavy slow down when going into dungeon rooms.

In Mercuris Chest, Dungeon 2:

• When pressing the button in the entrance room,
• It will call a special map function doing camera movements to open the front door.
• During this small cutscene, the hero is frozen.
• When going to the room up ahead, you will notice a small slow down as soon as entering the room (I think separators are part of the problem).
• Then strike the crystal.
• Go to the previous room, the slow down will not be here anymore.
• Go to the room on the right, push the button and get the key in the chest.
• Leaving that room will cause a bigger slow down of the engine but going to the south of that room will speed up to catch up time.

To me:

• Separators, camera, movements, hero state and probably surface draw calls and shader effects are all part of the problem. But not those separately.