Cell contents are missing when the header size is assigned through the e.Size property of the HeaderSizeEventArgs in the HeaderSizeNeeded event handler of RadVirtualGrid.
This happens only for some of the cells and when the viewport has many rows and columns.
To work this around, instead of setting the header size in the HeaderSizeNeeded event handler, use the ColumnWidth property of RadVirtualGrid.
<telerik:RadVirtualGrid ColumnWidth="50" />
Currently, to modify the default appearance of the cells you can use the CellDecorationsNeeded event of RadVirtualGrid. The event args exposes a predefined set of properties that can be applied onto the cell. However, there is no text alignment.
Introduce a cell text alignment property in the event args similar to the CellTextAlignment of the RadVirtualGrid itself.
This component will have the goal to achieve fast operations when dealing with millions of records from a data source. This should be accomplished by decoupling the UI logic from data management operations like loading, filtering, sorting and grouping which should be delegated to the server. Since the grid will not have ItemsSource property, the developer will be responsible for managing the data to/from the server through a given events. Official version of RadVirtualGrid is available from R3 2017 Release of UI for WPF. Check what's new in R3 2017 here: http://www.telerik.com/support/whats-new/wpf/release-history/ui-for-wpf-r3-2017