To reproduce:
public RadRibbonForm1()
{
    InitializeComponent();
    radRibbonBar1.Expanded = false;
}     

private void button1_Click(object sender, EventArgs e)
{
    if (ribbonTab2.Visibility == Telerik.WinControls.ElementVisibility.Visible)
    {
        ribbonTab2.Visibility = Telerik.WinControls.ElementVisibility.Collapsed;
    }
    else
    {
        ribbonTab2.Visibility = Telerik.WinControls.ElementVisibility.Visible;
    }
}

Workaround:
private void button1_Click(object sender, EventArgs e)
{
  
    this.radRibbonBar1.RootElement.SuspendLayout();
    if (ribbonTab2.Visibility == Telerik.WinControls.ElementVisibility.Visible)
    {
        ribbonTab2.Visibility = Telerik.WinControls.ElementVisibility.Collapsed;
    }
    else
    {
        ribbonTab2.Visibility = Telerik.WinControls.ElementVisibility.Visible;
    }
    this.radRibbonBar1.RootElement.ResumeLayout(false);          
}