Ahah. Was just about to give up and found the solution on StackOverflow.
Need to create the option and pass that to the field first, because ajax.
new Option('label', 'value', true, true);
Creates and sets the value. Huzzah!
if ($("#acf-field_5dcc4aa906709").find("option[value=" + selectedValue + "]").length) {
$('#acf-field_5dcc4aa906709').val([selectedValue]).trigger('change');
} else {
// Create the DOM option that is pre-selected by default
var newCounty = new Option(county, selectedValue, true, true);
// Append it to the select
$("#acf-field_5dcc4aa906709").append(newCounty).trigger('change');
}
Turns out I am having a different issue that is breaking the page.
But that function is still having an error.
in acf-field-groups.js addProLocations function.
ProLocationTypes is null but its object type is still an object. So the Object.entries function is triggering an error.
Ive narrowed this down to a problem with BuddyForms. If I remove the field from the frontend form it works, but when I add it back in, it does not…
I was having the same issue. I did a hard refresh on a wp-admin page and all is working again.