When one world has been opened and closed, the second opening of a world (whether it be a newly created, the same or a different world), will result in a world that 'spazzes' or 'flimmers''. It's as if the generation of the world fails, and it switches between parts of chunks for any number of different parts all the time. Fixed items in the vicinity (flowers, chests, animals etc) stay fixed, and you can interact with the world, but you can't see the world, as it constantly changes.
As a second part of this, once the first world is exited, the background music playing in the launcher/start screens (when choosing a new world) seems to be running double, but out of sync.
The issue resolves itself by closing and relaunching Minecraft completely.