Is it typo for "90-logout-button"? You need to use "f90-logout-button".
We have checked the issue at your website. You have placed logout button in Top menu as well as in Sidebar Menu. Sidebar menu is working but Top Menu is not working because your template is not applying css class " f90-logout-button" in the Top menu link.
You should contact to your template provider or menu module provider (if you are using any third party module for this) to fix this issue.