Would you please share some more details on how have you defined the template with ComboBox? Would you ensure you have not placed RadGridView in a control which measures it with infinity (i.e. StackPanel, ScrollViewer, Grid.RowDefinition with Height Auto)? Generally, I would not recommend you defining RadGridView (or any virtualized control) in such a container as it measures its content with infinity and the UI virtualization of the grid will be broken. Consequently, there will be performance degradation. You can also check our online documentation explaining how the UI virtualization works.
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Feedback Portal
and vote to affect the priority of the items