Identify occluders

Hi,

I am debugging a scene where a camera don't render some objects while it should. I managed to reduce the scope to an occluding problem. There are some occluders in front of the camera preventing it from rendering objects (see attached picture).

My issue is that I cannot find which objects are creating the occluders. Is there any way to find from the with the help of the occlusion debug where the occluders come from?

Also, what is the the camera Volumes? Why it is smaller than the camera frustum? This seems rather illogical because if Unity check occluders only in the Camera Volume it might miss some that are still in the frustum but not inside the Camera volumes..

For information I am running Unity 2020.3.11f1