The list items are duplicated in the target list after running incremental copy in the following two scenarios:
Scenario 1:
Full list copy using CSOM, then migrate incrementally with 0 days using Azure Turbo Mode.
Scenario 2:
Full copy list using Azure Turbo Mode, then migrate incrementally with 0 days using CSOM.
The tool functionality that helps to find the item on target that linked to item from source is different for CSOM migration and Azure Turbo Migration.
When using Azure Turbo we set the unique id field and use this unique id in future migrations for identifying linked item. However, this unique id cannot be set using CSOM. Because of this CSOM limitation we use another property for storing the unique ID of the source item and use it in future *Incremental* migrations to identify the linked item.
We have to use different logic for CSOM migration and Azure Turbo migration because implementation for Azure (setting custom unique id) cannot be implemented for CSOM, and at the same time implementation for CSOM (setting 'MetaInfo' field value) cannot be implemented for Azure. As a result we have two different functionalities for finding linked items on target for migration and because of this only the same type of process (through Azure Turbo or CSOM) has to be used.
In other words,
