When you retrieve a message, though the retrieval is successful the body of the message is blank. However, all other fields (To, From, CC, BCC) and any attachments are present; only the body of the message is missing. The ArchiveOne service trace shows the following:
01 11:59:10 416067 @DCOM01731ef8 CAMComplianceServer::GetMessageToFolder returning entryid '(null)'
The message in this scenario has had single instance storage applied to it. Whilst reconstructing the message, an error occurs and the staged temporary data is lost resulting in a message with no body text.
This issue has been resolved in v18.104.22.16814 and later. You should upgrade to the latest version.