Can you confirm if you are using a Menu defined in Appearance > menu, and that this menu is indeed there.
If you are 100% sure that you have no child theme active and no plugins active, then something is messed up. I know akismet should not be the issue, but make a test deactivating ALL plugin just to be sure.
If you are indeed using a menu created in Appearance > menu and properly allocated to the menu bar in Appearance > Menus > Manage Location, I would try creating a New Custom menu in Appearance > Menus > Edit Menus, and switching your menu bar to this new menu in Appearance > Menus > Manage Location, to see if that makes a difference, in case your menu is corrupted.
Next step would be to redo the latest wordpress update in appearance Update.
Next step would be to save settings in Save Restore as well as download all settings from the same page, then switch to a different theme, Delete all weaver themes and plugins, and reinstall from scratch the Weaver Xtreme theme and the Weaver Xtreme Theme support plugin (all your settings should be back)