So let's select one of our balls, and Enable Emission on it, and change the HDR scale to 2.0 or 2.5
What's happening is that the Camera that is following and rotating around the camera is sometimes going into the volume box or going out of the volume box.
Also don't forget to put it on the Post Processing Layer!
Very important: If you want to use more than 1 volume, you cannot use Is Global tick button option. So they all must have that green box
While in Playmode, try adjusting the Shutter Angle to 0, and then back to a high number. You'll feel the difference, and then leave it at a number you think is good for you!
Move the Main Camera close to the player and then switch to Game View, and change your Depth of Field settings.