Hi Clintre,
Thank you for contacting us!
The reason for your case is that when you want to assign a task to ‘userId’ you need also to set the userList property to true.
I have tested the kanban component with the same data that you have and it works as it should.
Here is the code snippet of the kanban:

window.Smart('#kanban', class {
    get properties() {
        return {
            collapsible: true,
            dataSource: data,
            addNewButton: true,
            editable: true,
            taskActions: true,
            taskDue: true,
            taskProgress: true,
            userList: true,
            users: [
                { id: 0, name: 'Andrew' },
                { id: 1, name: 'Anne' },
                { id: 2, name: 'Janet' },
                { id: 3, name: 'John' },
                { id: 4, name: 'Laura'}
            columns: [
                { label: 'To do', dataField: 'toDo' },
                { label: 'In progress', dataField: 'inProgress' },
                { label: 'Testing', dataField: 'testing' },
                { label: 'Done', dataField: 'done' }

Let me know if that works for you!
Please, do not hesitate to contact us if you have any additional questions.
Best regards,
Yavor Dashev
Smart UI Team