This happened in the 1.14 pre-release 5 as well. Entire chunks are swapping with other chunks. Multiple worlds have had this issue for me. Started on another survival world but has happened on four total. Things that affect biomes such as leaf colors, grass colors, lighting, water color, and spawning of mobs have been switching with the chunks. Doesn't happen right away in the world, happens when I log off and save my game and come back about an hour after playing for a previous hour or so. Hasn't affected any builds but it's incredibly irritating to have the landscape ruined by swapping chunks and a chunk of a biome in another chunk. The only constant thing from the four worlds where this has happened to me is that there was a swamp biome in the vicinity.
(Screenshots won't upload.)