I updated from version 1.16.4-1.4.1 to version 1.16.4-1.5.1 and in a world created under the 1.4.1 version. A prairie biome from Biomes o' Plenty turned into a fungal jungle biome also from Biomes o' Plenty. I removed the 1.5.1 file and put the 1.4.1 file back in and the biome went back to being a prairie biome. Currently using BoP version 1.16.4-13.0.0.429.

https://github.com/Beethoven92/BetterEndForge/issues/3
Know issue, its called biome id shift, a common plague that curse all mods that add new biomes to the game