Footer and Watermark added by iTextSharp not appearing in Edge but OK in Chrome - pdf

Question

I create pdfs using iTextSharp and add a footnote and watermark to these using a PdfStamper. This has been working fine. Recently the footers and watermarks have not been appearing when the pdfs are viewed in MS Edge. However, if I view the same pdf in Chrome the footers and watermarks appear correctly.
I store the pdfs in blob storage in Azure.
I have recently changed iTextSharp version from V4.1.2.0 to V5.5.13.
The code for adding watermarks and footers is as follows:
Dim byteArray As Byte()
Using stream As MemoryStream = New MemoryStream
reportBlockBlob.DownloadToStream(stream)
reader = New PdfReader(CType(stream.ToArray(), Byte()))
If reader IsNot Nothing Then
Using stamper As PdfStamper = New PdfStamper(reader, stream)
Dim PageCount As Integer = reader.NumberOfPages
If bReportInvalid Then
For i As Integer = 1 To PageCount
StampWaterMark(stamper, i, "INVALID", fontReport60, 35, New text.BaseColor(70, 70, 255), reader.GetPageSizeWithRotation(i))
Next
ElseIf Not UserRoles.Contains(WaspWAVB.con.csUserRoleCertificateSignOff) Then
For i As Integer = 1 To PageCount
StampWaterMark(stamper, i, "DRAFT", fontReport60, 35, New text.BaseColor(70, 70, 255), reader.GetPageSizeWithRotation(i))
Next
End If
If bAddFooter Then
Dim sRepUCN As String = "UCN"
Dim sCopyright As String = "Copyright"
Dim yPos As Integer = 12
Dim xLeftPos As Integer = 36
Dim xMidPos As Single = 297.5
Dim xRightPos As Integer = 559
For i As Integer = 3 To PageCount - iAppendixCount
ColumnText.ShowTextAligned(stamper.GetOverContent(i), text.Element.ALIGN_LEFT, New text.Phrase(sRepUCN, fontMedium), xLeftPos, yPos, 0)
ColumnText.ShowTextAligned(stamper.GetOverContent(i), text.Element.ALIGN_CENTER, New text.Phrase(sCopyright, fontMedium), xMidPos, yPos, 0)
Dim rttnPg As Integer = reader.GetPageRotation(i)
If rttnPg <> 0 Then
xRightPos = 806
End If
ColumnText.ShowTextAligned(stamper.GetOverContent(i), text.Element.ALIGN_RIGHT, New text.Phrase(String.Format(WaspWAVB.con.csPageXofY, i - 2, PageCount - 2 - iAppendixCount), fontMedium), xRightPos, yPos, 0)
Next
End If
End Using
byteArray = stream.ToArray()
End If
End Using
reportBlockBlob.Properties.ContentType = "application/pdf"
reportBlockBlob.UploadFromByteArray(byteArray, 0, byteArray.Length)
Public Shared Sub StampWaterMark(ByRef stamper As PdfStamper,
ByVal i As Integer,
ByVal watermark As String,
ByVal font As text.Font,
ByVal angle As Single,
ByVal color As text.BaseColor,
ByVal realPageSize As text.Rectangle,
Optional ByVal rect As text.Rectangle = Nothing)
Dim gstate = New PdfGState()
gstate.FillOpacity = 0.1F
gstate.StrokeOpacity = 0.3F
stamper.GetOverContent(i).SaveState()
stamper.GetOverContent(i).SetGState(gstate)
stamper.GetOverContent(i).SetColorFill(color)
stamper.GetOverContent(i).BeginText()
Dim ps = If(rect, realPageSize)
Dim x = (ps.Right + ps.Left) / 2
Dim y = (ps.Bottom + ps.Top) / 2
ColumnText.ShowTextAligned(stamper.GetOverContent(i), text.Element.ALIGN_CENTER, New text.Phrase(watermark, font), x, y, angle)
End Sub
I have tried re-arranging the order in which the footer and watermark are applied and commenting out either the addition of watermark or footer. None of this helps.
I use the code to add a footer elsewhere in the code and this works. Where it works, the footer is applied to an individual page. Where it doesn't work I have just collected together pages stored in separate blobs and amalgamated them into one memorystream. The footer and watermark are applied to this.
What is mystifying is that the pdf works fine in Chrome but not in Edge. This works either way round - i.e. if I create it in Chrome and view it in Edge, the footers disappear and if I create it in Edge and view it in Chrome, the footers appear.
Has anyone else seen this problem and knows how to solve it?