Mobs not aggressive, not pathfinding, not moving on slabs

I built ilmango's drowned farm- https://www.youtube.com/watch?v=5ZCBqjvMtNs - but the Drowned that spawn not only don't pathfind to the turtle egg I placed, they won't even pathfind to me, and won't even attack me when I'm stood right in front of them and even if I attack them, with one exception- see below video.

Video evidence- https://youtu.be/w81SW32N7QE . The only one that got aggressive was the one with the trident, and only when I hit it first, though testing this in a creative world, a trident-wielding Drowned will get aggressive toward a villager, but not any other kind. I can spawn a zombie next to a villager with a spawn egg and it won't make any attempt to attack the villager. A mob spawned with a spawn egg will also remain non-hostile if spawned on a half-slab, but will be hostile if spawned on a full block. I can make the world download available if necessary.