When deleted a component in the in world component editor, that name cannot be used for another component until the editor has been restarted.
1. Open editor using UE4Editor.exe QAGame
2. Place Barrel_02 static mesh into the level
3. Convert to Class Blueprint
4. Add a Point light component
5. Name the component "Light"
6. Delete the point light component
7. Add another point light component
8. Name the new component "Light"
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-8651 in the post.