To verify this issue it will be necessary to capture a Dtrace of the EvSharePointArchiveTask process.
{SHAREPOINTWALKER.EN_US} Not doing shortcut processing because library is a Records Center library: http://sitecollection/site/subsite/DropOffLibrary
Shortcut processing does not create shortcuts in a Sharepoint library because this library is considered a Records Center library by Enterprise Vault.
Enterprise Vault does not create shortcuts in a Records Center library, or a library that uses a template with the Records Center library attributes (a list of libraries where Enterprise Vault does not create shortcut can be found in the ‘Setting Up SharePoint Server Archiving’ guide.). To see if the Hold feature has been enabled on a particular SharePoint site go to Site Settings->Features:

If the SharePoint Admins have deactivated this feature, or it does not show as Active then it is still possible for EV to report that the site is a records center. When performing Shortcut processing Enterprise Vault will look at the holdlistid attribute of a Site, if this property is not null then this site is considered a Records Center. One way to verify this is with the following Sharepoint Management Shell command:
(Get-SPWeb -Identity 'https://sitename/subsitename').AllProperties
[Example of the output]

It is up to the SharePoint admin's to resolve this issue. Known workarounds are: