The description for Horizon Falloff is misspelled, it says 'Horitzon' instead of 'Horizon'.
Edit MattK: This is a content issue because this is a blueprint data variable.
1. Open a blank template
2. Highlight the SkySphereBlueprint
3. Look for 'Horizon Falloff' in the Details of the SkySphereBlueprint
Head over to the existing Questions & Answers thread and let us know what's up.