Blocks broken by flowing fluids do not activate sculk sensors
MC-25976 is likely to be the bug causing this; I'd recommend trying to fix that one first to see if the issue resolved itself as a result.
Sculk sensors are intended to detect the breaking of blocks as valid vibrations. This works for manually broken blocks, however if a block is instead broken by a fluid flowing into its place, the block is destroyed without the sculk sensor picking up vibrations as a result.
The expected behaviour would be that the sculk sensor would in fact pick this up as a vibration, since a block is obviously being broken.