After upgrading ArcGIS Data Store, validating a relational data store in ArcGIS Server fails, returning the following error message:
Error: Failed to update federated server. 'https://gisserver.domain.com:6443 (id: <ID_Number>)'. Failed to validate the server managed database '/enterpriseDatabases/AGSDataStore_ds_<DataStoreID>'.
Portal for ArcGIS logs may display errors related to the PostgreSQL databases.
ArcGIS Data Store was corrupted during the upgrade process, and did not complete the upgrade process correctly. This results in two different versions of the PostgreSQL database being present in the ArcGIS Data Store local machine directory, preventing ArcGIS Server from validating the data store.
Restore ArcGIS Data Store to an earlier backup point. Refer to How To: Restore ArcGIS Data Store for the steps to do this.