Nintex Errored Workflow Report shows workflows where the item has been deleted
The Nintex Admin report "Errored Workflows" shows workflows where the item has been deleted.
This is because the workflow record within the Nintex Content DB isn't updated to show that the item has been deleted or the site has been removed.
In order to resolve this, run the NWAdmin.exe -o SyncTerminatedWorkflows -url teamsiteurl [-terminateDeletedItems]
The parameter -[-terminateDeletedItems], will identify any records where the item has been deleted, and will mark the workflow as cancelled. This will then suppress the workflow instance from being shown in the Errored Workflows admin report.
In order to remove the records, run the NWAdmin Purge Workflow History and Workflow data command and target any workflows that are cancelled.
See the following document for further details of the command: