Currently filtering with virtualized RadComboBox is not supported as the filtering feature works with the containers (changes their Visibility).
Create NuGet symbol packages - containing the .pdb files - corresponding to the primary NuGet packages. The process is described here: https://docs.microsoft.com/en-us/nuget/create-packages/symbol-packages . This will facilitate the debugging of problems in the controls code.
InvalidOperationException when closing a RadWindow opened on a separated UI thread. The exception message is: "Cannot use a DependencyObject that belongs to a different thread than its parent Freezable."
To work this around, you can merge the Telerik.Windows.Controls.Navigation.xaml dictionary in the Resources of all RadWindow instances open on another thread and then set their Style property to the RadWindowStyle from the merged .xaml dictionary.
<telerik:RadWindow x:Class="WpfApp84.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WpfApp84" xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation"
mc:Ignorable="d" Height="450" Width="800" Style="{DynamicResource RadWindowStyle}">
<telerik:RadWindow.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/Telerik.Windows.Controls.Navigation;component/Themes/GenericWindows11.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</telerik:RadWindow.Resources>
</telerik:RadWindow>
Empty cells appear when the RadGridView contains many cells in the viewport and the view gets resized.
To work this around you can extract and modify the ControlTemplate of GridViewCell, in order to set the MinHeight property of the "PART_ContentPresenter" element to a number close to the RowHeight of the RadGridView control.
The fly view is not properly displayed when the second item is clicked and the sub-items are expanded (see attached video).
Attached is a project with a workaround as well.