I had created a survival world in 1.17, recently opened it in 1.18 and was struggling to find an ocean so I used /locatebiome to find one. When I went to the coordinates the command gave me it is in the middle of a forest. My assumption is that this has something to do with the game generating new terrain underground for the new caves, causing the specified biome to get changed? The terrain it thinks is an ocean is also not new, it was generated in 1.17.