VaultWiki does not work correctly on XenForo when the setting "Name of the Wiki Route" is given a blank value. This is fixed in the next release.
Until the next release, you will have to use a non-empty value for this setting.
If the setting is not blank, but you had XenForo's default route set to /wiki prior to 4.0.13, that setting value actually did nothing in earlier versions. As of 4.0.13, it works. But if you were using it already, then your wiki's URLs are now wrong. In this case, you will need to rebuild your wiki's URLs in AdminCP > Wiki > Maintenance > Rebuild Counters / Caches.