It seems RadGridView is measured with infinity in this scenario. Generally, I would not recommend you defining RadGridView (or any virtualized control) in panels like ScrollViewer
as they measure its content with infinity and the UI virtualization of the grid will be broken. Consequently, there will be also performance degradation.
You can place RadGridView in a Grid with Row.Height="*"
instead. You can also refer to the online documentation
explaining how the UI virtualization
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