Mobs pathfinding tells them that partial blocks are safe, when in fact they fall through them. It allows for easy ways to trick mobs into falling off edges or into pits. Glitches a handful of non-normal sized Blocks:
Slabs
Beds
Trapdoors
and Others
This can also lead to other odd bugs, as Zombies can't jump onto trapdoors that are on the bottom of the block one above them, even though they player can. They just treat it as if it were an open block, and stand with their hands raised. (see picture)
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While I am fully aware this is not the cause of your issue, you should update your Java. The current Java for Minecraft on OS X is 1.8.0_60. You are two major revisions behind. Again, I know this doesn't affect your report in any way.

My computer can't handle the new Java very well. I had updated once, and it corrupted some of my old files, hints why I'm still at this version.
If it were easier to uninstall Java back to it's old version on a Mac, I'd try, but it took a long time to get it back to 6 to un-corrupt my files.

That doesn't sound right, but so long as you are aware.

Updated for latest Snapshot, Torches and non-collider blocks seem to be fixed.

Isn't this the same as MC-157645 ?
Affects 20w12a.
Can confirm in 21w05b.
Can confirm in 21w07a.
Can confirm in 1.16.5 and 21w08b.

Please specify the problem with "Slabs, Beds, and Others".