Consider Contacts data before upgrade to EPiServer Commerce 8.6.1
We faced an issue in deploying EPiServer Commerce 8.6.1 to our live environment where we have about 2 million users. Up gradation failed on Migration and got an error in result
Updating contact data has failed with exception 'System.Data.SqlClient.SqlException (0x80131904): Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.
We contacted EPiServer support and they were very helpful as always, they provided us a script as a hotfix to run on dBs for migration, that probably update required data through SQL Server management studio and in result rest of the migration goes smoothly. This issue have already been fixed in latest versions.