Minecraft 1.20.1 - Forge 47.3.7 - Alex's Mobs 1.22.9

Yeah I am also getting this issue. I've even gotten as many as three sunbirds spawning within close proximity to each other, all of which are just hovering there.

Edit: I would like that this is likely due to their pathfinding breaking either because they were spawned when out of a loaded chunk, or because they are trying to pathfind to a unloaded chunk. I'm not entirely sure. All I know is that it seems like their pathfinding AI just fails to work frequently.