I have had multiple crashes that all start with some Alexs Mobs entity ticking/rendering and causing the game to crash. Its happened with Orcas, Roadrunners, Emus, and a variety of other mobs, and they all seem to have the same sort of crash report. I cant make any sense of them, maybe you could, though.

Emu Render:
crash-2021-08-18_17.53.10-client.txt

Bald Eagle Tick:
crash-2021-08-18_17.02.18-server.txt

Fly Render:
crash-2021-08-18_15.08.08-client.txt

Orca Render:
crash-2021-08-14_21.20.56-client.txt

Roadrunner Render:
crash-2021-08-14_20.13.26-client.txt

I'm getting the same issue. The mod has crashed my game several times. I cannot re-enter a world once it has crashed.

Here's my latest crash report.

I've also been unable to respawn in these worlds. I don't know if that's caused by the same issue.

I have the exact same issues. A temporary fix is to delete all the files in world\entities, but this also removes other entities.