When there is custom template applied that hosts multiple rows of UI components with total height greater than 44, the template is not measured correctly, leading to wrong visualization.
When CollapseAll method is called, if the first element is out of the screen (after a scroll), the treeview crashes. Available in minor release 2018.3.1109. It will also be available in the R1 2019 release.
Currently this could be accomplished through methods.
Calling TreeView's CheckItem method when the control is loaded, so that you mimic a "pre-checked" TreeView results in NullReferenceException in RadTreeView.Checkbox ToggleItem method.
Available in R3 2018 release.
Expose a BringIntoView or ScrollIntoView method that would scroll the TreeView to a specified TreeViewItem. Available in R3 2018 release. For more details on the feature refer to: https://docs.telerik.com/devtools/xamarin/controls/treeview/treeview-scrolling