It appears that the natural generation of snow layers in Extreme Hills biomes and such uses a 32-bit float in its generation somewhere, causing it to break somewhat when far from the origin. This can be seen in vanilla by teleporting over 16777216 blocks out, preferably on both axes, and finding an Mountains biome (or just generating a custom world with exclusively Mountains) - any areas that would have had patchy areas of snow in vanilla will now be slightly more angular than they would normally be, being composed of more straight lines and squares.
This - versions prior (13w36a to 15w51b) are completely unaffected by this. For example, here's a screenshot of 1.8.2-pre4 (left) and 1.15.2 (right), with seeds provided:
I am not sure if this bug can cause crashes like