xConnect log errors Batch Execution Exception "AlreadyExists, Contact"

Question

A brand new local XP0 developer install of Sitecore 9.1 continually throws the following errors in the xConnect logs:

2018-12-11 20:43:33.928 +08:00 [Error] Sitecore.XConnect.Operations.AddContactOperation: Sitecore.XConnect.Operations.EntityOperationException: Operation #0, AlreadyExists, Contact
2018-12-11 20:43:33.929 +08:00 [Error] Sitecore.XConnect.Operations.SetFacetOperation`1[Sitecore.XConnect.Facet]: Sitecore.XConnect.Operations.FacetOperationException: Operation #1, ReferenceNotFound, Contact, Classification
2018-12-11 20:43:33.929 +08:00 [Error] ["XdbContextLoggingPlugin"] XdbContext Batch Execution Exception
Sitecore.XConnect.Operations.EntityOperationException: Operation #0, AlreadyExists, Contact
2018-12-11 20:43:33.929 +08:00 [Error] ["XdbContextLoggingPlugin"] XdbContext Batch Execution Exception
Sitecore.XConnect.Operations.FacetOperationException: Operation #1, ReferenceNotFound, Contact, Classification

Sitecore XP website logs are clean and data is appearing in analytics. There is no custom code at all. Marketing definitions deployed, indexes rebuilt, but the error remains. Any suggestions ?

Thanks

Answer 1

This was caused by installing after a prior installation which had failed, without deleting the SOLR indexes. Removing SOLR indexes and reinstalling fixed the issue.

Answer 2

The above answer suggests that you delete and reinstall the SOLR indexes, but that is a pretty heavy-handed approach to resolving the issue. For anyone who wants an easier approach, just do the following:

1. Log into Sitecore Admin as an administrator.
2. Go to Control Panel.
3. Under the Indexing section, click Indexing Manager
4. Select all indexes associated with Marketing, Suggested, Personalization. If you want to rebuild all to be safe, that's fine too, it just may take more time.

As of writing this, I am using Sitecore 10.3.