Some items in list Documents were not successfully migrated "Go to Reports to download and view the error log for this list to review the files that were skipped or failed to migrate in this migration task." (4381097)

In some migrations, the migration tool reports that certain items from a SharePoint list or document library were not migrated. The reported mismatch typically shows a one-item difference between the “Source Item Count” and the “Discovered Item Count.”
However, when verified directly in SharePoint or by exporting items from the source library, the number of discoverable items matches the “Discovered Item Count,” not the “Source Item Count” reported by the Client-Side Object Model (CSOM).

This can cause confusion, as the migration report suggests a failure when all available items were actually migrated successfully.

This behavior is due to a known issue with Microsoft SharePoint Online where:

• The CSOM (Client-Side Object Model) API sometimes returns a slightly higher item count than what is actually retrievable in the source list.
• The “SharePoint Contents” page may display one more item than what can be enumerated or exported programmatically.
• This inconsistency causes migration tools relying on CSOM counts to report a mismatch, even though no real item loss occurs.

• This issue is cosmetic and does not indicate missing or failed items during migration.
• Verify by exporting or enumerating items directly from the source list or library; the actual item count will match the “Discovered Item Count.”
• No corrective action is required as long as the verified item counts align.
• Microsoft has acknowledged this behavior as a known SharePoint API limitation that may occasionally occur during item discovery.