100s of duplicate contacts created of current user when using CiviCRM
I have seen this when the uf_match table does not have the proper values for WP Id (uf_id), Contact ID (contact_id) and email (uf_name).

I don't know why this occurs, I've not been able to track it down, but I suspect it is when the uf_id and contact_id do not have the email in use by WP.  

You can user API Explorer /wp-admin/admin.php?page=CiviCRM&amp;q=civicrm/api to display the records or do a query on the civicrm_uf_match table.   

To fix, I have deleted the 'bad contacts (merging if data needs to be retained) and then updating the uf_match records so this does not re-occur.