Mismatch on customer entity on data migration followed by an integrity constraint violation on delta migration

[Andreabont]

Preconditions

1. Source

   • Magento Community Edition 1.9.0.1

2. Destination:

   • Magento Community Edition 2.4.5
   • Data Migration Tool 2.4.5
   • MySQL 8.0
   • PHP 8.1

Steps to reproduce

1. Data migration: bin/magento migrate:data [path to config] -r -a with a concurrent user registration.
2. Delta migration: bin/magento migrate:delta [path to config] -a

Expected result

The delta migration sync Magento 2 with the data of Magento 1

Actual result

The delta migration fail with the SQL error:
SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '[...]@[...]-0' for key 'customer_entity.CUSTOMER_ENTITY_EMAIL_WEBSITE_ID', query was: INSERT INTOcustomer_entity (entity_id,website_id,[...]

Additional notes

I'm trying to migrate a Magento 1 website (in use in production), to Magento 2.
I setup a migration plan following this documentation: https://experienceleague.adobe.com/docs/commerce-operations/tools/data-migration/how-migration-works.html?lang=en

The data migration finished successfully, but with this warning:
[2023-02-27T11:46:45.766434+00:00][WARNING]: Mismatch of entities in the document: customer_entity Source: 202998 Destination: 202997

I thought a user signed up during the migration, so I did a delta migration, but a database error stopped the process:
SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '[...]@[...]-0' for key 'customer_entity.CUSTOMER_ENTITY_EMAIL_WEBSITE_ID', query was: INSERT INTOcustomer_entity (entity_id,website_id,[...]

[m2-assistant]

Hi @Andreabont. Thank you for your report.
To speed up processing of this issue, make sure that you provided sufficient information.
Add a comment to assign the issue: @magento I am working on this

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