Issue:

Player can walk into half slabs and suffocate in them

Player can also walk through chests (suspended 1 block above the ground)

Replicate:

Walk though a 1.5 high gap (slabs on top) and you will suffocate in them

Suspend a chest 1 block off the ground and walk through it

Expectation:

Player should not move through a half slab

Player should not be able to walk through chests