Very simple. I see this after the world has been loaded for a while.

https://gist.github.com/MuteTiefling/a67dfe3a0807021cbea43bd393131f1c

I'm not sure what to make of it, or if there is something I need to change in my configurations.

Right now, all I'm doing with JED is setting my spawn point to that dimension (dim 1008), enabling some vanilla game rules, and disabling the end/nether...

Dimensions config: https://gist.github.com/MuteTiefling/c40e52cb70835cc18b5ddad8fe8318f7

So I've just been informed that I wasn't using JED 1.6, so there's a good chance this is already fixed. I'm updating and will test. I'll close this up for now and re-open if anything.

That crash will likely still happen, as your config causes JED to use its own WorldInfo object for that dimension. That should be fixed on Advanced Rocketry's side by checking the type of the WorldInfo object before assuming that it's the vanilla DerivedWorldInfo.

Definitely still happening. I'll leave this closed for now and report to AR,