My game has crashed twice today with the same error, while batching chunks.

Crash report: https://pastebin.com/Fn3Q0FKV

Game loads fine afterwards with seemingly minimal or no lost progress, it's just annoying.

I have this very same issue.
java.util.ConcurrentModificationException: null

Five instances of crashlogs in the following gist:
https://gist.github.com/Jack-McKalling/49d5b75804a6d1ca28bce7fc529019a2

Versions:

• Pack: 1.3
• Create: create-mc1.16.5_v0.3.2g
• Forge: 1.16.5-36.2.20
• Optifine: no