Cascaded selctpicker dropdownl ist no resetting

I have a cascaded dropdown list using json to populate second dropdown and also using slectpicker to search for data in the second dropdown list. The problem I have is that the second dd is not resetting on change

I use asp.net core and Razor pages

View

    

        
            Selecteaza sursa de pericol
            Executant
            Sarcina de munca
            Mijloace de productie
        
        
        
    
    

        
            Selecteaza pericolul
        
        
        
    
    

        
            --Selecteaza Forma de manifestare--
        
        
    

json

public async Task OnGetCategorieAsync(string id)
{
    var categorie = await _context.FactoriRiscs.Where(s => s.Sursa == id).Select(s => s.Categorie).Distinct().ToListAsync();

    return new JsonResult(new SelectList(categorie, "Categorie"));
}

public async Task OnGetFormaManAsync(string id)
{
    var forma = await _context.EvarisMains.Where(s => s.Pericol == id).Select(s => s.FormaManifestare).Distinct().ToListAsync();

    return new JsonResult(new SelectList(forma, "FormaManifestare"));
}

jquery

$(function () {
    $("#Sursa").on("change", function () {
        var categoryId = $("#Sursa :selected").text();
        $("#Categorie").empty();
        $("#Categorie").append("--Selecteaza o categorie--");
        $.getJSON(`?handler=Categorie&id=${categoryId}`, (data) => {
            $.each(data, function (i, item) {
                $("#Categorie").append(`${item.text}`);
            });
        });

        var data = $("#Sursa :selected").text();
        $("#txtSursa").val(data);
    });
});

$(function () {
    $("#Categorie").on("change", function () {
        var categoryId = $("#Categorie :selected").text();
        $("#FormaM").empty();
        $("#FormaM").append("--Selecteaza forma de manifestare sau adauga--");
        $.getJSON(`?handler=FormaMan&id=${categoryId}`, (data) => {
            $.each(data, function (i, item) {
                $("#FormaM").append(`${item.text}`);
            });
            $('#FormaM').selectpicker({ liveSearch: true });
        });

        var data = $("#Categorie :selected").text();
        $("#txtCategorie").val(data);

    });
});