I think crabs suffocate out of water. They all start to get ticking damage and just die.
I do play with a large mod list and I have heavily modified the modfiles to make the animals spawn on Regions Unexplored biomes. Maybe that is part of the issue.

Running the newest version with the reworked crabs.

You're still having this issue on 1.3.2?

Just realized that I was running 1.3.0 and not the newest version. You updated so fast, I could not catch up.

Thank you and sorry for my outdated report!