Excel VBA insert tags around italicized strings

I'm new to VBA and trying to write a script that inserts XML tags around italicized text in Excel. I discovered this question: VBA Excel Changing Italics and adding </ and />

The first answer has a clever approach and I'm modifying that code. It works as is for the first italicized string in a cell, but not for subsequent strings.

Here is the code I'm trying. It loops through each character until it finds the first Italics and inserts a tag and turns the lngCount variable to True. When it finds regular text, if the lngCount variable is True, it inserts the end tag and resets the variable to False.

It works perfectly in some cells, but in other places it doesn't insert the end tag, it others it doesn't insert any tags. Since I can't figure out any consistent differences to when it works well and doesn't, can anyone help? Am I misunderstanding anything about vba?

Sub EmphTags()
    Dim lngStart As Long
    Dim lngFinish As Long
    Dim n As Long
    Dim rngCell As Range
    Dim rngConstants As Range

    On Error Resume Next
    Set rngConstants = ActiveSheet.UsedRange.SpecialCells(xlCellTypeConstants)
    On Error GoTo 0

    If Not rngConstants Is Nothing Then
        'Application.ScreenUpdating = False
        For Each rngCell In rngConstants.Cells
            lngCount = False
            lngStart = 0
            lngFinish = 0
            For n = 1 To Len(rngCell.Text)
                If rngCell.Characters(n, 1).Font.Color = 0 Then
                    If rngCell.Characters(n, 1).Font.Italic Then
                        If lngCount = False Then
                            lngStart = n
                            rngCell.Characters(lngStart, 0).Insert "<emph render='italic'>"
                            rngCell.Characters(lngStart, 22).Font.Italic = True
                        End If
                        lngCount = True
                    ElseIf lngCount = True Then
                        lngFinish = n
                        rngCell.Characters(lngFinish, 0).Insert "</emph>"
                        rngCell.Characters(lngFinish, 7).Font.Italic = False
                        lngCount = 0
                    End If
                End If
            Next n
        Next rngCell
        'Application.ScreenUpdating = True
    End If
End Sub