The reason I ask about the default theme, is because there might be an error cause by your theme that breaks the store locator, and the only way you can find this out, is by switching to a default theme.
I get this js error when I open the page in Firefox, and that will break the store locator. When you are logged in, it probably loads the vendor.js instead of the vendor.min.js.
Timestamp: 14/09/2015 13:20:45
Error: NS_ERROR_NOT_AVAILABLE:
Source File: https://www.wepositive.eu/wp-content/themes/north-wp/assets/js/vendor.min.js
Line: 1
You can try to find where the vendor.js is loaded, probably in the functions.php, and see if makes it a difference if you always make it load the vendor.js file. If you can’t find it in the function.php, just search all the files in the north-wp folder for ‘vendor’, or contact the theme author, and ask him to fix it.