Reverb Volumes unreliable

I use Reverb Volumes to muffle sounds when underwater. I find that often a sound will play inside the volume and no LPF is applied to it. It seems totally intermittent.

If I repeatedly swing my axe while underwater, the swinging sound will often not play at all, play but with no LPF, or play with the correct LPF applied.

Does anyone know why these reverb volumes seem to be so unreliable?