After upgrading from Enterprise Vault (EV) 8.0 to Enterprise Vault (EV) 9.0, opening archived items through Outlook Web Access (OWA) Search Archive times out and returns the html version of the item. However, when opening through OWA Archive Explorer, the item is retrieved successfully and is displayed correctly.
This is caused by double url encoding in the saveset id. This leads to the OWA extensions using the wrong name to check if the item has been restored, which causes the restore to fail. When a restore of an item retrieved in OWA fails, the default method to render the messages is via EV rather than OWA, in an HTML format.
This issue has been addressed as part of the following release:
Enterprise Vault 9.0.3 - Release Details
Enterprise Vault 10.0.1 - Release Details