Parent form sometimes does not close (Only in Windows 10) - vb.net

Question

My main form is frmInvoice. This sub is located inside frmInvoice.
This is one of the Subs that sometimes causes frmDark to not close. frmLookup does not display when this happens. frmDark just stays there covering frmInvoice. It's like it doesn't reach the call to frm.ShowDialog(frmDark), cause when I press the lookup key, it displays the frmLookup, but upon closing frmLookup, frmDark is still there.
No exception is being raised.
Note that this only happens in Windows 10. In Windows 8/7, this never happened. What am I missing?
This happens at different times. Sometimes I could press the lookup key for 20 times and it will display fine. Sometimes, after 1 press of the lookup key and this happens.
Private Sub ItemLookup()
Try
Using frmDark As New Form
With frmDark
.ShowInTaskbar = False
.Icon = Me.Icon
.FormBorderStyle = Windows.Forms.FormBorderStyle.None
.BackColor = Color.Black
.Opacity = 0.95
.WindowState = FormWindowState.Maximized
.Show(Me)
Using frm As New frmLookup
With frm
.Icon = Me.Icon
.ShowDialog(frmDark)
frmDark.Close()
If .DialogResult = Windows.Forms.DialogResult.OK Then
' Do stuff here
End If
End With
End Using
End With
End Using
Catch ex As Exception
ErrMsg(ex)
End Try
End Sub
UPDATE: I'm using .Net Framework 4.8
Thanks

Answer 1

I would suggest rearranging the code like so:
Dim lookupResult As DialogResult
Using frmDark As New Form With {.ShowInTaskbar = False,
.Icon = Me.Icon,
...}
frmDark.Show(Me)
Using frm As New frmLookup With {.Icon = Me.Icon}
lookupResult = frm.ShowDialog(frmDark)
End Using
End Using
If lookupResult = DialogResult.OK Then
'...
End If
Because that code exits the Using block that created frmDark, there should be no way that it can't close.
Also, instead of using a vanilla Form and configuring it on demand, I would suggest that you create a dedicated form type to use as the overlay in that scenario. You can then get rid of all the property assignments.
Having a dedicated overlay form would also allow you to reconfigure things significantly and, in my opinion, better. The overlay form could have a property of type Form. You main form could then create a frmLookup instance and assign it to that property, than call ShowDialog on the overlay form. In the Shown event handler of the overlay form, it could then call ShowDialog on the form in that property. When that call returns, it could assign the result to its own DialogResult property and close itself. The main form would then just get the result from calling ShowDialog on the overlay. That might look like this:
Public Class OverlayForm
Public Property DialogueForm As Form
Private Sub OverlayForm_Shown(sender As Object, e As EventArgs) Handles Me.Shown
DialogResult = DialogueForm.ShowDialog()
End Sub
End Class
and this:
Public Class MainForm
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Using dialogue As New DialogueForm,
overlay As New OverlayForm With {.DialogueForm = dialogue}
If overlay.ShowDialog() = DialogResult.OK Then
MessageBox.Show("OK")
End If
End Using
End Sub
End Class