Some VaultWiki code has requested the DataRegistry's 'addOns' entry, which usually contains an array of addon IDs and their version IDs.
XenForo's DataRegistry model is responsible for fetching, unserializing, and returning that array to VaultWiki. However, XenForo is not able to unserialize this standard entry because it contains a date string instead of the expected serialized array.
The problem is with the contents of this DataRegistry entry. So your problem lies somewhere else.