TreeView is in dropdowncontent of a DropDownButton. BringPathIntoView is called on loaded of the button (or the tree). It tries to bring several nested levels deep for example item 90.3.2.1 (4 levels deep).
On opening the button , the scrollviewer is not scrolled to the desired item.

Posssible workarounds:

 - invoke the BringPathIntoView method in a Dispatcher.BeginInvoke call

 - disable the treeview animations before the call and enable them after the call ( telerik:AnimationManager.IsAnimationEnabled = False)