There are 2 boss bars when you come close to one. Before it wakes up it looks like it is only one, because they spawn in the exact same location. But when it notices you and it stands up it divides in two. This didn't happen once but three times, in the minecraft:snowy_tundra biome. I am playing with the version 1.15.18 of the mod, and have many other mods installed.

Duplicate of #395
Please remove BGCore until they fix the issue.