The world border doesn't seem to render properly; or at the very least, it doesn't render well at night due to the rendering changes. Instead of a constant green-ish color while still, blue while moving, etc. like before, the world border seems to depend on the current fog color- this causes the world border to be difficult to see at night.
in the screenshots, I am testing on a floating island world set to the lush caves biome, but I'm pretty sure this bug will just as easily occur on any other world type. I set the world border to a mere 301 blocks here.