Title. The logs seem to complain about concurrentModificationException, which I think is an error when two mods try to edit the same thing? So probably a conflict. Thought you'd want to know about it regardless.
Here's my log: https://mclo.gs/nPfv4JE
Let me know if I need to provide any other info. I keep forgetting to turn on emails for github notifications though, so I might take a while to respond.

If you remove ndu does it still happen?

Removing NDU fixes the crash, yes.

Could you try if this fixes it
netherdepthsupgrade-3.0.0-1.18.2.zip

I tried, and it did! Thanks!