Base page is only created on main site in WordPress Multisite
The default behaviour of CiviCRM on WordPress Multisite is that the base page is not created on every site on which CiviCRM is activated. Instead, the base page is only auto-created on the main site. The absence of the base page on a sub-site can lead to confusion - however it may be the desired behaviour when the WordPress Multisite instance is one where sub-sites are not truly "separate" e.g. sites built on frameworks such as Commons in a Box or MultilingualPress.
Proposed fix: auto-create the base page on all sites on which CiviCRM has been activated but allow plugins to enable the legacy switch to the main site behaviour.