Has been working good - nothing changed and suddenly this error notification.
Even refactoring the razor page no change
<div class="col-md-12">
<RadzenDataGrid @ref="grid0" ColumnWidth="200px" AllowFiltering="true" FilterMode="FilterMode.Advanced" AllowPaging="true" AllowSorting="true"
Data="@vertrag" Count=count LoadData=@Grid0LoadData TItem="ImpulsStammdaten.Server.Models.AntragVertrag.Vertragkomplett" RowDoubleClick="@EditRow">
<Columns>
</Columns>
</RadzenDataGrid>
</div>