I was playing nicely today when, suddenly the game stopped responding.
I could still walk around, open inventory, but all mobs stopped walking around and my backpack (from traveler's backpacks) was not opening.
Then I saw this on log window:

15:47:14.905   game   [16:47:14] [Server thread/WARN] [FML]: GottschCore loaded a new chunk [-158, 56] in dimension 0 (overworld) while populating chunk [-157, 56], causing cascading worldgen lag.
15:47:14.906   game   [16:47:14] [Server thread/WARN] [FML]: Please report this to the mod's issue tracker. This log can be disabled in the Forge config.

Then here I am. Wrinting this while waiting for my game world to close, but it is taking too long. I guess I'll just stop the game's process.

I hope there's a solution.

Here is the full log file:
https://gist.github.com/InterPlay02/60372c41a6d65376bcfbb38a0122c75f