Dual-write does not work with the cross company data sharing policies in D365 FinOps (there are so many names but I am using this name for reference ).
Brief overview about cross company data sharing policy first to set the base for the readers, the Cross-Company data sharing lets you have your data accessible from multiple legal entities (companies in D365 FinOps). For example, if you setup a policy for vendors to be crossed-company then whenever you create a new vendor it will be created in all data sharing legal entities.
Now, What happened when you a table under cross-company data sharing (e.g. VendTable) and want to sync vendors through dual-write?
Since, VendTable is one of the data sources for Vendors data entity (dual-write entity map) and we know dual-write does not work well with cross-company data sharing by design. You get following error message when you try to Run the entity map.
"Copying pre-existing data completed with errors. For additional details, go to initial sync details tab."
The error message is confusing and does not reflect the actual issue behind the scene - you will never be able to figured it out what is wrong until you raise it with MS dual-write team and share the activity Id of the job with them to investigate the telemetry (you don't have access to check this one ) then they share the root cause.
However, You can also investigate by putting a breakpoint in method validateDataSharingEnabledForEntityTableBeforDualWriteEnable() of class SysDataSharingValidation.