For me, the Underwater fx causes glitches. I tried to change the buffer, but nothing changes.
Underwater causes a background crackling on my track - I was using it for a temporary glitch effect. It took me ages to work out what was causing the crackling. I solved it simply by automating it to turn on only when i wanted the glitch. Previously I’d left it running but with the dial right back. While I was diagnosing the problem, it seemed to be associated with mid-bass tracks, but I realised later that it wasn’t the tracks causing the problem, but simply the frequency range.