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" />