Script Include - Glide AJAX enabled - not working?

ver. Yokohama, PDI - I was  following steps found here: https://youtu.be/fcHhxT_f7T8

Exploring Dynamic Filter Options, followed his steps, exactly, but it does not work. It ONLY works if I select Sandbox enabled on the Script Include. It doesn't work when Mobile callable or Glide AJAX enabled are selected. Why? What's going on here?

Script include:

// Glide AJAX enabled [x]
var myPrimaryAssignmentGroup2 = Class.create();
myPrimaryAssignmentGroup2.prototype = Object.extendsObject(AbstractAjaxProcessor, {

	getAssignmentGroup: function(user) {
        var gr = new GlideRecord('sys_user');
        gr.addQuery('sys_id', user);
        gr.query();

        var grp;

        if (gr.next()) {
            grp = gr.u_primary_assignment_group;
            gs.log("MyGroup: " + grp);
        }
        return grp;
    },
    type: 'myPrimaryAssignmentGroup2'
});

This works as a Background script, even if "Sanbox enabled" is not selected. What's happening here?

var dfo = new myPrimaryAssignmentGroup2().getAssignmentGroup(gs.getUserID());
gs.info("Assignment group: " +dfo);`

Anyone else seeing this?