I've isolated the problem to Optifine. Currently, the 1.11.2 version (Every variation available on their website) of Optifine causes worlds to not load. With any other mod or mod combination I've used, the game starts up fine, the worlds load fine, the game itself runs well. Anytime I put Optifine into the mix, the game starts up fine, I can use the shaders or resource packs I want, but the moment I try to open up any of my worlds, with or without shaders, with or without resource packs, with or without other mods, the game crashes before the world loads. Here's my most recent crash log with no other mods and "Internal" shaders on. The world was pre-loaded in vanilla Minecraft outside of Forge.