The resource of specified task within the single PWA site in Project Server on Premise cannot be updated

Question

I tried to extract specific task from particular project to update the Resource/ Assignment. The following sample code is for my testing. I perform this in Console .NET framework and no error. Unfortunately, no changes happened in the Task assignment. The scenario will be, Task A was assigned to any personal named PERSON A, and now I want to add or change to another person named PERSON B. I have tried a lot of workarounds on this issue. But never work. If you have any solutions, please let me know, that will save more time for me. Thanks a lot once again.

// Load the draft project
var draftProject = project.Draft;
context.Load(draftProject);
context.ExecuteQuery();

// Load the tasks and project resources
context.Load(draftProject.Tasks);
context.Load(draftProject.ProjectResources);
context.ExecuteQuery();

// Find the specific task
var task = draftProject.Tasks.FirstOrDefault(t => t.Name == Params.PWA_TASK_NAME);

if (task != null)
{
    // Load the assignments for the task
    context.Load(task.Assignments);
    context.ExecuteQuery();

    // Load the Resource property for each assignment
    context.Load(task.Assignments, assignments => assignments.Include(a => a.Resource));
    context.ExecuteQuery();

    // Find the assignment
    var assignmentToUpdate = task.Assignments.FirstOrDefault(a => a.Resource.Name == "000 New Local Resource");

    if (assignmentToUpdate != null)
    {
        // Load the resources with their Ids and Names
        context.Load(draftProject.ProjectResources, resources => resources.Include(r => r.Id, r => r.Name));
        context.ExecuteQuery();

        // Find the resource
        var resourceToUpdate = draftProject.ProjectResources.FirstOrDefault(r => r.Id == assignmentToUpdate.Resource.Id);

        if (resourceToUpdate != null)
        {
            // Display the resource name
            Console.WriteLine("Resource Name: " + resourceToUpdate.Name);

            // Update the resource name
            resourceToUpdate.Name = Params.PWA_LOCAL_RESOURCE_NAME_4;
            context.ExecuteQuery(); // 提交更改到服务器

            // Save changes to the draft project
            draftProject.Update();
            context.ExecuteQuery(); // 提交更改到服务器
        }
        else
        {
            Console.WriteLine("Resource not found.");
        }
    }
    else
    {
        Console.WriteLine("Assignment not found.");
    }
}
else
{
    Console.WriteLine("Task not found.");
} 

Try to know what the root cause is. or how to resolve this.?