dhtmlXCombo in ajax call not working

I have a dhtmlXCombo box that is populated after an ajax call, but I can’t initialize it. It’s always empty.

after the ajax call this code is run

//my select list this.resourceTypeCtrl

        this.PopulateDropdownList(this.resourceTypeCtrl, data.resourceTypes);

        var myCombo = dhtmlXComboFromSelect("gantt-filter-resource-types");

and here is the PopulateDropdownList function

PopulateDropdownList(dropdown, options) { for (var i = 0; i < options.length; ++i) { var opt = options[i]; var el = document.createElement("option"); el.textContent = opt.name; el.value = opt.id; dropdown.appendChild(el); }; }

The Select list is being populated, however when I try to convert it to dhtmlx combo it does not populate. That is from an existing select.
I have also tried with a DIV

var myCombo = new dhtmlXCombo("gantt-filter-resource-types"); for (let i = 0; i < data.resourceTypes.length; i++) { myCombo.addOption(data.resourceTypes[i].id, data.resourceTypes[i].name, null); }[/code]

This also doesn’t work.

The problem with thedropdown is the z-index. It has a z index of 116 or something like that