Hi,
in the last update select field search allow multiple values, so you can search for example for values "Drenthe" and "Frevoland" at the same time.

Now you see a normal HTML select with "multiple" attribute, this happened because you have disabled "jQuery Chosen" via CSS (https://www.easy-profile.com/support/two-differents-select-buttons.html).

You can:
1) remove "multiple" attribute via Javascript by adding this simple javascript code:

jQuery(document).ready(function(){

    jQuery('.jsn_search #jform_provincie').removeAttr('multiple');

});

2) Re-enable "jQuery Chosen" (https://www.easy-profile.com/support/two-differents-select-buttons.html)

Thanks!