Same happened to me:
Coords: -140 60 -1650
Seed: 366659953681281981Its a warm Ocean Biome (Release 1.17)
I have the same problem, and I am Using Optifine too, didn't think about it, that it could be Optifine, causing this Problem. I will test a bit without Optifine, if it happens too, I will submit a new bug report.
There you have it, yes it is on a Chunck border
Same happened to me:
[media]Coords: -140 60 -1650
Seed: 366659953681281981
Its a warm Ocean Biome (Release 1.17)