I believe this is caused by changes in the nether's surface generation, which might have something to do with the surface rules.
In noise generation stages, it still generates the bedrock like it usually would,
but at the surface generation stage these bedrock layers get replaced by regular surface blocks (which does not happen in 21w42a).
Making sure that these surface terrain generation stages cannot replace bedrock blocks fixes this issue
Can reproduce with both regular and calibrated sculk sensors.
They no longer give the advancement for just moving around whilst sneaking, you now have to trigger other game events like falling whilst sneaking to trigger it.