Multiple problems with terrain including-
Floating blocks/islands
High walls and corners on chunk borders
Entire chunks missing snow or ice
Floating grass
Odd mineshaft generation in mesa biomes
Snow and desert biome generation next to each other
Everything seem too course and needs to be smoothed out a little.
All screenshots taken by myself was done in a single freshly generated world using Minecraft 1.13-pre1 with seed: 1453522920
Most of this looks normal, the rest are duplicates.