In my single player survival world, i have a few plant farms that I have decorated, and one of those farms that I have decorated, I put slabs on top of full blocks, (essentially making it 1 and a half blocks tall, it seems to attract nearby mobs (mostly passive mobs) and those mobs will continuously jump up and down toward the slab. I have had this problem with cows, sheeps, wandering trading Llamas, horses and also iron golems. I tried pushing them back away from the slab but that doesn't help.