In the file

ext.pf.select2.combobox.js

Line 157, the variable

data

is set as an object.
In Line 158 it gets checked if its an array.

if ( Array.isArray( data ) )

This is always false and no data is added to the autocomplete values array.

I propose to check for an object instead

if (Object.keys(data).length !== 0) {
	for (var key in data) {
		values.push({
			id: data[key], text: data[key]
		});
	}
}