In the following screenshot from a Lotus Notes client, it is possible to see the 'empty' box supposed to contain the items related to the thread/conversation

In iNotes / DWA, 'No conversation history' appears above the message header
The "Display / Thread", "Display / Conversation" or "Show / Hide mail threads" actions actually reveal the content of the hidden views '$ThreadsEmbed' or '(Mail Threads)' (depending on the action and version), and these views are embedded with a setting to show the content of the current thread only, associating the open item to its parent and response documents via its UniversalID.
During the retrieval of an item archived by Enterprise Vault, the item shown to the users is actually a new temporary item, created in the Domino mail file of the user, with its own new UniversalID (as the original item / shortcut also still exists in the mail file with the original UniversalID), and therefore the embedded conversation history view remains empty as the item cannot be associated by UniversalID to its original parent and response documents.
The following workarounds can be used to view the conversation history of an item archived by Enterprise Vault:
There are currently no plans to address this issue by way of a patch or hotfix in the current or previous versions of the software at the present time.
This issue may be resolved in a future major revision of the software at a later time. However, this particular issue is not currently scheduled for any release. If you feel this issue has a direct business impact for you and your continued use of the product, please contact your Veritas Sales representative or the Veritas Sales group to discuss these concerns.
For information on how to contact Veritas Sales, please see https://www.veritas.com