Case Management Data Import error:Could not enrich party by alternative key(s): Retrieved Id is null

Summary:

As per business requirement trying to import case management data through Import Management. During data validation receiving error: ERROR: Could not enrich party by alternative key(s): Retrieved Id is null: AltKey With Value [527327] , Retrieved Id With Value [null]

I have queried and verified that alternate key person_number: 527327 exists and there is valid person id.

Sample file attached.

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