I think I just saw another issue related to this. I might have not looked hard enough but I didn't see the same cause. Anyways this happens after I have searched for a biome.
https://gist.github.com/Wohlf-craft/3db2111db80092fb1e91c57f7811a0c2

Edit: I forget to mention but I am using a standard forge server. Latest forge and version of the mod. I don't know if it works with other mods or not.

Just to confirm, you are using version 1.6.2? Thought this issue was fixed in that version.

Would you mind posting the crash report crash-2019-12-16_17.52.53-server.txt?

No I have the version on 1.6.0

Please update to 1.6.0 and let me know if the problem is resolved.

I was running a modpack with 1.6.0 and manually updated it to the newest version and that fixed it.

Marking this as resolved, in that case