If you use WPML, and some store locations show up more than once in the search results, then this is probably because not all the translated locations have the same latitude and longitude values.

You can check this on the Store Locator > All Stores page and edit the different translations for the location that shows up multiple times.

Scroll down to the “Store Details” section, select the “Location” tab, look for the latitude and longitude fields, and make sure the values are identical for all the translated locations.