This is not a BC issue. It was present in Sewer Sewer during early access. However we briefly touched on it in the BC coMmunity stream and I failed to offer useful advice. So I thought we should revisit it here and offer some tips.
On further investigation I found that each section of the sewer has a trigger zone detecting the camera. If the camera is detected the sewer section is powered on (collidable). If the camera is not detected the sewer section powers off, loses collision and the player falls out of the level.
My initial suggestion would be to control the visibility of the sewer sections not the power. As by turning off the visibility the objects retain their collision.
This doesn't solve the camera potentially going out of the pipe and hiding it at the wrong time though. Possibly making the zone a little wider would help this.