WinForms TreeView AccessViolationException

Question

In a Windows Forms application multi-targeted to Core 6 and Framework 4.8, I'm using a TreeView control to select a subform to host in a neighboring panel control. At various points, I call the following function on the main form to build and rebuild the tree nodes:

Public Sub UpdateFormSelection(procEnt As ProcessEntity)  
        treeFormSelection.BeginUpdate()         'control won't repaint until EndUpdate is called  
        treeFormSelection.Nodes.Clear()  
        If Not IsListNothingOrEmpty(procEnt.Forms) Then  
            FormListToNodes(treeFormSelection.Nodes, procEnt.Forms)     'recurse!  
        End If  
        If (procEnt.CurrentForm IsNot Nothing) Then  
            treeFormSelection.SelectedNode = treeFormSelection.Nodes(procEnt.CurrentForm)  
        End If  
        treeFormSelection.EndUpdate()  
    End Sub  
  
Private Sub FormListToNodes(currentNodeList As TreeNodeCollection, formList As List(Of WizardForm))  
        For Each form As WizardForm In formList  
            If form.IsSelectable Then  
                Dim currentNode As TreeNode = currentNodeList.Add(form.TabName)  
                If Not IsListNothingOrEmpty(form.Children) Then  
                    FormListToNodes(currentNode.Nodes, form.Children)       'recurse!  
                    currentNode.Expand()  
                End If  
            End If  
        Next  
    End Sub  
  

At one point, I have one of the subforms change the IsSelectable property for another, then call UpdateFormSelection. The second subform appears or disappears as directed. I can change my displayed form as normal, by selecting a new node from the treeview, but within a few selections, an AccessViolationException is called.

I can't be trying to access the missing form, as I'm getting the form name to access from the treeview itself. The stack trace is as follows:

 	[Managed to Native Transition]	  
>	System.Windows.Forms.Primitives.dll!Interop.User32.CallWindowProcW(System.IntPtr wndProc, System.IntPtr hWnd, Interop.User32.WM msg, System.IntPtr wParam, System.IntPtr lParam)	Unknown  
 	System.Windows.Forms.dll!System.Windows.Forms.NativeWindow.DefWndProc(ref System.Windows.Forms.Message m)	Unknown  
 	System.Windows.Forms.dll!System.Windows.Forms.Control.DefWndProc(ref System.Windows.Forms.Message m)	Unknown  
 	System.Windows.Forms.dll!System.Windows.Forms.TreeView.WmMouseDown(ref System.Windows.Forms.Message m, System.Windows.Forms.MouseButtons button, int clicks)	Unknown  
 	System.Windows.Forms.dll!System.Windows.Forms.TreeView.WndProc(ref System.Windows.Forms.Message m)	Unknown  
 	System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.OnMessage(ref System.Windows.Forms.Message m)	Unknown  
 	System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.WndProc(ref System.Windows.Forms.Message m)	Unknown  
 	System.Windows.Forms.dll!System.Windows.Forms.NativeWindow.Callback(System.IntPtr hWnd, Interop.User32.WM msg, System.IntPtr wparam, System.IntPtr lparam)	Unknown  
 	[Native to Managed Transition]	  
 	[Managed to Native Transition]	  
 	System.Windows.Forms.dll!System.Windows.Forms.Application.ComponentManager.Interop.Mso.IMsoComponentManager.FPushMessageLoop(System.UIntPtr dwComponentID, Interop.Mso.msoloop uReason, void* pvLoopData)	Unknown  
 	System.Windows.Forms.dll!System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Interop.Mso.msoloop reason, System.Windows.Forms.ApplicationContext context)	Unknown  
 	System.Windows.Forms.dll!System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Interop.Mso.msoloop reason, System.Windows.Forms.ApplicationContext context)	Unknown  
 	System.Windows.Forms.dll!System.Windows.Forms.Application.Run(System.Windows.Forms.ApplicationContext context)	Unknown  
 	Microsoft.VisualBasic.Forms.dll!Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun()	Unknown  
 	Microsoft.VisualBasic.Forms.dll!Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel()	Unknown  
 	Microsoft.VisualBasic.Forms.dll!Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(string[] commandLine)	Unknown  
  

I tried writing a simplified demo of the code, but it didn't cause the same error.

It should be noted that node that was selected prior to updating the treeview is deselected, and attempting to reselect it immediately after the update causes the treeview to select other nodes, apparently randomly. Selected a different node causes the form to update properly until the AccessViolationException is throw.

Additionally, I am handling the treeview DrawNode event. I set the draw mode back to normal to see if that caused the problem, but it didn't seem to have an affect.

Any thoughts on how to hunt this down?