Description
When running the Find Similar Locations tool, the candidate features must have at least two unique features. These features must be unique, as well as the reference location.
Solution
Make sure that there is enough variety in your attributes of interest for your candidate features, and that at least two of these feature have different attribute values from your reference locations. If you are using more than one reference location, make sure there are at least two candidate features with different values than the averaged values of the reference location.