This warning may occur when you copy an element from the main model to a design option.
Issue: In this case, the element exists in the main model and in the design option. As a result, these 2 elements overlap.
Solution: To resolve the issue, delete the element from the main model or from the design option.
If you tried to move an element from the main model to a design option, cut the element from the model (instead of copying the element), or use the Add to Set tool.