I got this code (from somewhere, maybe here) that returns the items selected on a pivot filter.

Function ShowReportFilterItems(rng As Range)
    Application.Volatile (True)
    myfield = rng.Value
    a = rng.PivotTable.Name
    With rng.PivotTable.PivotFields(myfield)
     N = .PivotItems.Count
        For i = 1 To N
          If .PivotItems(i).Visible Then
         s = s & " " & .PivotItems(i).Name & "."
         End If
        Next i
    End With
    ShowReportFilterItems = s
    
End Function
UDF works fine, it recalculates when I change the filter and when I refresh the pivot BUT I also have a macro initiated by a button that refreshes the pivot (pivot is somewhat hidden, that is why I need the button). The macro is simply: 
Sub refresh_rank_pivot()
    ActiveSheet.PivotTables("PivotTable7").PivotCache.Refresh
End Sub
SO, when I refresh the pivot via the button i get a #Value! error. If I reculc (full or F2 enter on one of the cells containing the UDF) it works fine again.
Can anyone please explain, resolve?