This will only be applicable if you configure the Change Guardian integration.
All attachment data in the system need to be migrated so that for Change guardian events, on clicking the Shield icon, Diff and Delta attachments will be loaded. After upgrading Sentinel (from prior to the 8.5.1.0 version), if the partitions that are having attachment data are not migrated, then the existing data will not be supported to display Diff and Delta attachments. Hence, the results of CG reports will be inconsistent.
For example, for reports that have information for the past three months, the attachment data for that period must be migrated, before starting report jobs. Else, the generated reports might not be accurate.
After upgrading Sentinel, migration is required only for the existing (old) attachment data and not for the new attachment data.
You can migrate attachment data through an offline tool.