Spawn chunks unload. Many systems rely on spawn chunks being always loaded, like automatic farms. There is no config option to turn this off either.
Using the latest release from CurseForge: VanillaFix-1.0.10-150
Minecraft version 1.12.2
Forge 14.23.5.2855
I'm sorry that this is a duplicate, but there is no config option to turn this feature off.

There's no config option to turn it off, but can you verify that the 1.12.2 version actually unloads spawn chunks? I can't reproduce, and it looks like this feature wasn't added until version 1.1. https://github.com/DimensionalDevelopment/VanillaFix/releases/tag/1.1

Edit: Looks like this behavior is hidden behind the B:bugFixes config setting, which had been set to false in my install. It would still be nice to have a separate config option brought for this in 1.12 though so you don't have to disable the bug fixes as a work around.

Hi, I can verify. New 1.12.2 minecraft install.

1. Only VanillaFix installed: Spawn chunks stay loaded.
2. VanillaFix and Optifine installed: spawn chunks unload. (Note that Smooth World option is OFF.)
3. Only Optifine installed: spawn chunks stay loaded.
   So if both Optifine and VanillaFix are installed, spawn chunks unload.

EDIT: I set B:bugFixes to false and the problem disappeared, with both Optifine and VanillaFix installed. Thank you for finding the config option, and yes a dedicated config option would be great.