If it's the Cycle Map layer you have a problem with, Cycle Map (also CyclOSM and the Transport Map layer) is rendering the coastline as it was mapped *before* the changeset I mentioned! Those layers are not updated as frequently as the "Standard" layer.

As for tagging the intertidal area here as *not* a beach, I can't really comment as I don't know the area. That's particular to each "beach"/area of sand. The writer of the wiki states it's whether the area is "wave formed" or not.