Did you upgrade VaultWiki AFTER upgrading to XenForo 2.2.1? There is a different VaultWiki download for XenForo 2.2 than for earlier XenForos.
Some other things that could be happening:
- HTTP server passing incorrect values to PHP, such as for
$_SERVER['HTTP_HOST'] or
$_SERVER['SCRIPT_NAME']. Based on other reports I've had, the behavior of incorrect values may have changed in XenForo 2.2 or another recent version. This could lead to the wiki router not working. There are some directions here about testing if this is the problem:
https://www.vaultwiki.org/issues/6098/
- If friendly wiki URLs are active, and if certain settings were modified while the VaultWiki add-on was disabled, the database table vw_path might be empty or incorrect, causing the wiki router not to work. You can regenerate the table in AdminCP > Wiki > Maintenance > Rebuild Counters / Cache > Rebuild Content URLs.
If neither of those work, please submit a ticket here:
https://www.vaultwiki.org/members/?do=newticket
We would need to access the forum/files to see what's wrong.