When i load up my server (Airplane-Purpur) without any plugins other than the herobrine one and no datapack it causes a biome changing. For example the plains and forest became ocean (with F3 and also the grass color changed) and a part of the savanna also changed in ocean biome. The seed is: graviola (and i also use the latest version of the plugin and the latest version of airplane-purpur server jar).
Well, this is a new problem that I've never heard of before. Are you sure you are not using any other plugins? I cannot think of a reason for why the plugin would mess with your world biome. Can you share some screenshots please?