latest.log
My game is heavily modded, I'm not sure if it's an incompatibility-related error. My mods are listed in the log.
I've tried editing the .Jar, which fixed the error, but I completely forgot what I did, and accidentally overwritten it, so I'm back at square one.
It doesn't crash Minecraft, just the world itself. It happens every time I try to load any world, regardless of what I do.
UPDATE: I fixed it! It wasn't Origins at all! it was Origins++. I forgot it needs XL Packets and doesn't install automatically with the mod

Closed as op has mentioned that they solved it.