I open the game with Optifabric just fine but the second I open a world, for whatever reason I'm greeted to an entirely black screen. I can still interact and close out of the world, but I can't even see the escape screen until I'm back to the main menu. No clue why this is happening

Which mods are you using? This sounds similar to what Satin can do with shaders turned on but OptiFabric shouldn't let that happen any more.