I have a somewhat large modpack (404 mods), and there is chunkloading errors litterally everywhere. like, even after pressing f3+a, they still remain, and like, i can say that theres more chunkloading errored chunks then not. i have fastcraft installled, moving around large distances seems to load a bit of them, but other than that, i cant see what could be causing it. i have fastcraft, optifine didnt seem to do much when i had it installed.