Failed to Upsert Data into Lakehouse Delta Table – Missing System.Linq.Async Assembly

Hi All,

While ingesting data from an on-premises SQL Server database table into a Lakehouse Delta table in Microsoft Fabric using the upsert method in copy activity, I encountered the following error:

ErrorCode=FailedToUpsertDataIntoDeltaTable, 'Type=Microsoft.DataTransfer.Common.Shared.HybridDeliveryException, Message=Hit an error when upsert data to table in Lakehouse. Error message: Could not load file or assembly 'System.Linq.Async, Version=6.0.0.0, Culture=neutral, PublicKeyToken=94bc3704cddfc263' or one of its dependencies. The system cannot find the file specified., Source=Microsoft.DataTransfer.Connectors.LakehouseTableConnector,''Type=System.IO.FileNotFoundException, Message=Could not load file or assembly 'System.Linq.Async, Version=6.0.0.0, Culture=neutral, PublicKeyToken=94bc3704cddfc263' or one of its dependencies. The system cannot find the file specified., Source=Microsoft.DataTransfer.Connectors.LakehouseTableConnector,'

Steps to reproduce:

1. Configure pipeline to copy data from on-prem SQL Server to Fabric Lakehouse Delta table using copy activity.
2. Use Upsert method.
3. Run the pipeline.
4. Error occurs during execution.

Expected behavior:
The pipeline should upsert data into the Lakehouse Delta table without assembly-related errors.

Actual behavior:
The pipeline fails with the missing assembly error for System.Linq.Async.

Environment details:

• Source: On-premises SQL Server
• Destination: Fabric Lakehouse Delta table
• Copy activity with Upsert enabled

Request:
Please investigate and advise on:

• Whether this is a known issue with the Fabric Lakehouse connector
• Any non-Notebook workarounds (e.g., configuration change, library update, alternative method)
• ETA for a fix if this is a product bug,

Thanks All,