I was playing in a survival world and went AFK for a quick minute and when I came back I noticed that there was a zombie in my base (It's not very protected at the moment.) But this zombie was acting strange. It noticed me when I got closer to it, but it didn't start chasing me. It just stayed there and acted as if it were a mime with a wall in front of it even though there wasn't anything in front of it. It was just standing on some stairs that were right behind some lower half slabs.

      So I went to kill it but then decided to do some experimenting on  it. So I tried hitting it and that didn't do anything. Then I tried hitting it onto the slabs, but it ran right back over to the stairs as if he had some irrational fear of half slabs. So I tried it again and the same thing happened. After that I just killed him. 

      I was also able to make it happen consistently. I grabbed another zombie from outside of my base and led him to my base to the stairs and the same thing happened. He stopped at the stairs like there was an invisible wall. This time however I punched him far enough so he stayed on the slab rather than head back towards the stairs. Now he is stuck there, not able to move or pay attention to me. (There will be a screenshot of this as well)

     I just wanted to bring this bug to attention so that it can be fixed. If I do more experimenting and find interesting results, I will put them as an update in the post. Thanks for reading!

 [Update]

I did some testing with some other mobs by luring them to my base and here's what I found:

Zombie Villagers, Drowned, Pigs, Cows, Sheep, Chickens, Endermen, and Creepers all have the same issue with pathfinding as the zombie does. I also tried it with a spider but the spider was able to pathfind perfectly fine. These results lead me to hypothesize that there is a bug when it comes to pathfinding between stairs and lower half slabs with most mobs in general. (I didn't want to attach screenshots with all of the mobs that I tested out but it is basically the same issue as the first screenshot in the post. I'll put a picture of the Enderman trying to get me because it is the most interesting.)