So my mod Tilled soil has an issue where ancient dangers spawn totally empty.
After some lengthy testing I found that if you add a floor with <designationCategory>X</designationCategory>, where X is any value, and the floor has either no <costList> or an empty cost like <costList><Steel>0</Steel></costList> then ancient dangers are totally empty.
They will spawn and give you the warning, but when you open them and the interior spawns there is nothing inside.
After some lengthy testing I found that if you add a floor with <designationCategory>X</designationCategory>, where X is any value, and the floor has either no <costList> or an empty cost like <costList><Steel>0</Steel></costList> then ancient dangers are totally empty.
They will spawn and give you the warning, but when you open them and the interior spawns there is nothing inside.