Mobs in general will not walk over short blocks (ones that are shorter than a full block, like daylight sensors). This issue has been fixed for some common blocks (like lower slabs) but not for most other blocks. This is best seen when there is only air below the short block.

Currently affected short blocks: Grind stones, beds, lecterns, stone cutters, chest, daylight sensors, end portal frame, ender chests, bells, unlit campfires, chains, conduits, and end rods.
And probably other short blocks that i forgot about

How to reproduce.
1. Go 30 blocks off the ground, and make a 1 wide by 10 long row of blocks
2. Spawn a zombie on one end, and a villager on the other end
3. Between the mobs place a couple of the above mentioned blocks in the floor
4. Neither mob will walk over the above mentioned blocks
5. Sometimes mobs can pathfind over the blocks, however, its not really.. reliable? they will often jump around, stagger, stop, or fall off the block. Best seen with the grind stone.

Expected result:
Mobs would walk over and pathfind across these blocks with little to no issue.

Full demonstration, and explanation of this bug coming soon

Not a duplicate of MCPE-47075, that report was only for slabs/soul sand/brewing stands/enchantment tables. This is a related post for all other short blocks