Just started up a new world and the portal starts us out underground. Figured it was an accident, so we went to some stairs to go above ground and it takes us to another part of the same cave. Travelling via the stairs again leads to a separate instance of caves. This happened again after resetting the server, and after returning to the options menu, it says Caves twice instead of Forest and Caves.
Forest preset was saved to preset one, and then cave preset was also saved to preset one. so maybe this is what caused it?
Video shows what happened and all the mods / presets
made a new server, used custom presets, both forest and cave accidentally saved to preset 1