Hi. If you use aggregates in the grid and also apply localization (ej.base.setCulture or ej.base.setCurrencyCode), then when executing the query (dm.Aggregates), an error "System.ArgumentException: Duplicate type name within an assembly" occurs:
If we abandon the totals, or localization, the error does not occur. Keep in mind, an error occurs when using .NET Core v3.0.0-preview3. The example in the attachment.
P.S. It can also be noted that the error occurs only in debug mode (F5). Without debugging (Ctrl + F5) the error does not occur.