I'm using Alex's mobs on 1.18.2 and I've encountered two extreme bugs.
The first one has to do with the straddleboard and I found that it can easily be duplicated when broken while someone is standing on it.
The other is actually gamebreaking and it's that when I put the leviathan through a portal created by a dimensional carver it got duplicated to an extreme, like it wasn't just one or two it was dozens of leviathans spawned out of nowhere crashing my game and I currently am figuring out a way to get back in the world.