If you have your databases in an SSDT database Project you can use T4 templates to generate CRUD procedures.  I've also used written T-SQL to generate them, but since I...

Have you considered using SSRS and putting a page break based on customer id and save as a PDF or as Excel?

Can you post the table definitions including collation for character columns?

If your import table has a case-sensitive collation and your destination table does not you could still get...

Here's how I get Foreign Key info:

SELECT
  FK.name,
  SCHEMA_NAME(FK.schema_id) AS schemaName,
  OBJECT_NAME(FK.parent_object_id) AS parentTableName,
  parentCols.name AS parentColumnName,
  OBJECT_NAME(FK.referenced_object_id) AS referencedTableName,
 ...

Okay, I didn't delve deeply into what was different because the row counts returned where in the 300K range.  Basically the difference is that when run in serial the query...