Oh wait nevermind, that is just “regular” Worldgen Lag, and sometimes the game will just refuse to acknowledge that your player character has moved to the border of loaded Chunks, which can only be fixed by exiting the game and re-entering it, sometimes requiring Task Manager to kill Minecraft if you cant exit.
Did you use the Default Config Pack linked on the Download Page? It disables superfluous Worldgen that does not actually do anything (except Lag and then get deleted anyways, like Ores for example).