Before_workflow_action on throw the screen is frozen

Hello,
for testing I have this simple script:

frappe.ui.form.on('Task',  {
    before_workflow_action: (frm)=> {
        frappe.throw('err');
    }
});

About one month everything works perfectly, but now when the error dialog is closed than screen is freezing with a gray color and it is totally unclickable. I have to reload the site for next steps.
Do you have the same issue, please?