I expected this bug to have been fixed easily, but have resorted to finally reporting it. Mobs attempt to jump over blocks that do not allow pathfinding over which includes fences, wall types, and blocks with a slab on top. I first noticed this in January 2019. The roots of the glitch seem to be pathfinding of mobs leads to an incorrect path on inaccessible blocks, making the mob become stuck in the loop of pathfinding to that specific block. The mob will continuously jump at that spot until killed or the blocks are destroyed.