Yes, your code is not returning anything if user do not have manage_options capability. Use like following
add_filter( 'fep_menu_buttons', 'fep_cus_fep_menu_buttons', 99 );
function fep_cus_fep_menu_buttons( $menu )
{
if( ! current_user_can('manage_options') ){
unset( $menu['new_announcement'] );
}
return $menu;
}