DateTime refresh problem

When launching my app, I display the date/time of the last modification of certain files via a PopupMenu. I launch a modification (a write) in the Button_Pressed event then I restart the display of information (with the same function as above), nothing happens! it’s always the same date/time that are displayed but if I change the index of my PopupMenu and put it back on the previous one, I have the time of the modification that is displayed!
I’ve been going around in circles for a while. An idea ?

Var f As New FolderItem
Var Date1 As DateTime
f = SpecialFolder.VariableLog.Child(MyPeriodicity)  //Path
If f <> Nil And PopupMenu3.SelectedRowIndex > 0 Then
  Date1 = f.ModificationDateTime
  LabelDateTimeScript.Text =  "Last modification "+ Frequency + " the " + date1.ToString
End If

Remove the menuitem and build a new one adding it back to the parent each time you update.