Component not shown or displayed

Hi,

In my Vaadin web application, left side has a main menu, at center content display area and on right side
a menu to perform actions.

On clicking one particular main menu item, some times the menu at right side does not appear.
while checking the count of menu items, those are displayed correctly.
While other main menu items are working fine.

I tried to debug but does not find the solution why this is happening only for that.

Please help me to solve this.

Thanks