Drowned and players can attack, and players can break blocks, through waterlogged upper slab.

Steps to reproduce

1. Load MCPE-155956 Through Slabs.mcworld
2. Press the button to spawn a villager in front of the chest.
3. Make sure the lever is turned on to repeatedly teleport the drowned away from the villager.
4. If the drowned's tridents lodge in the slabs, try flipping the lever off for a while or adjusting the coordinates that it teleports the drowned to. The behavior is inconsistent and seems to depend on precise angles.

Expected result

The slabs stop the tridents every time.

Observed result

Sometimes the tridents pass through the slabs.
Drowned kills through slab.mp4

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My character is being constantly attacked and taking damage from drowned while standing on a platform made from waterlogged upper slabs. It happens day or night. It is very frustrating.