Intermittent failure of worksheet macro to populate outlook "To" field - excel

Question

I have a workbook with a summary tab, with one row per client, each row containing variables that populate an email to that client. Each row is mapped to a separate tab using excel formulas (which also refers to a lookups tab, where I can update client information such as emails and names). Each tab contains a worksheet macro to pull information into an outlook email (code below). This works fine most of the time, but often the final emails to generate fail to populate the email "To" field. This happens most after making changes to the workbook. If I save, close and reopen the workbook, most (if not all) of the email "To" fields populate correctly. The first emails to generate are always fine, but at some point while generating they stop populating "to", then every email to generate after that point does not have the "to" field. It ranges from 10% to 100% of the emails populating "to" correctly.
The code below is on each of the tabs (usually about 50 clients/tabs/emails run). Any ideas on why this could be, and how to make it always work 100%? It seems like I might just be asking too much of excel, having them all run at once, maybe they need to run in sequence, I'm not sure. Any help appreciated!
Dim xRg As Range
'Update by Extendoffice 2018/3/7
Public Sub Worksheet_Change(ByVal Target As Range)
On Error Resume Next
If Target.Cells.Count > 1 Then Exit Sub
Set xRg = Intersect(Range("AA1"), Target)
If xRg Is Nothing Then Exit Sub
If IsNumeric(Target.Value) And Target.Value > 0 Then
Call Mail_small_Text_Outlook
End If
End Sub
Sub Mail_small_Text_Outlook()
Application.EnableEvents = False
On Error GoTo Handler
ListObjects("Table6").Range.AutoFilter Field:=1, Criteria1:= _
"<>"
Dim xOutApp As Object
Dim xOutMail As Object
Dim xMailBody As String
Set xOutApp = CreateObject("Outlook.Application")
Set xOutMail = xOutApp.CreateItem(0)
On Error Resume Next
With xOutMail
.To = Range("H2")
.CC = "billing#example.com; name#example.com"
.BCC = ""
.Subject = Range("C2") & " - (ID: " & Range("I2") & ") - " & Range("B2") & " Lightning Docs Usage & Billing"
.HTMLBody = "<font size=-0> Hello " & Range("G2") & ",<br/><br/>" & vbNewLine & vbNewLine & _
"Please review the following list of loan documents that were produced through our online system from " & Range("B2") & ". <br/>Your total bill for this month's documents is " & FormatCurrency(Range("F2")) & " (" & Range("E2") & " x " & FormatCurrency(Range("D2")) & "):</font>" & vbNewLine & vbNewLine & _
RangetoHTML(Range("Table6")) & vbNewLine & vbNewLine & _
"<br/><font size=-0>Please let us know within two business days whether your records match ours. If we do not get a response within this time frame, we will invoice you shortly thereafter. If your credit card is on file and we have a pre-existing authorization, we will charge your card on file and provide you with a copy of your paid invoice." & vbNewLine & vbNewLine & _
"<br/><br/>Thank you!</font><br/>" & vbNewLine
.Display 'or use .Send
End With
On Error GoTo 0
Set xOutMail = Nothing
Set xOutApp = Nothing
Handler:
Application.EnableEvents = True
End Sub
Function RangetoHTML(rng As Range)
' Changed by Ron de Bruin 28-Oct-2006
' Working in Office 2000-2016
Dim fso As Object
Dim ts As Object
Dim TempFile As String
Dim TempWB As Workbook
TempFile = Environ$("temp") & "\" & Format(Now, "dd-mm-yy h-mm-ss") & ".htm"
'Copy the range and create a new workbook to past the data in
rng.Copy
Set TempWB = Workbooks.Add(1)
With TempWB.Sheets(1)
.Cells(1).PasteSpecial Paste:=8
.Cells(1).PasteSpecial xlPasteValues, , SkipBlanks:=True, Transpose:=False
.Cells(1).Select
Application.CutCopyMode = False
On Error Resume Next
.DrawingObjects.Visible = True
.DrawingObjects.Delete
On Error GoTo 0
End With
'Publish the sheet to a htm file
With TempWB.PublishObjects.Add( _
SourceType:=xlSourceRange, _
Filename:=TempFile, _
Sheet:=TempWB.Sheets(1).Name, _
Source:=TempWB.Sheets(1).UsedRange.Address, _
HtmlType:=xlHtmlStatic)
.Publish (True)
End With
'Read all data from the htm file into RangetoHTML
Set fso = CreateObject("Scripting.FileSystemObject")
Set ts = fso.GetFile(TempFile).OpenAsTextStream(1, -2)
RangetoHTML = ts.readall
ts.Close
RangetoHTML = Replace(RangetoHTML, "align=center x:publishsource=", _
"align=left x:publishsource=")
'Close TempWB
TempWB.Close savechanges:=False
'Delete the htm file we used in this function
Kill TempFile
Set ts = Nothing
Set fso = Nothing
Set TempWB = Nothing
End Function
Private Sub Worksheet_Calculate()
Dim xI As Integer
Dim xRg As Range
Set xRg = Range("AA1")
On Error GoTo Err01
xI = Int(xRg.Value)
If xI = 1 Then
Call Mail_small_Text_Outlook
End If
Err01:
End Sub

Answer 1

First of all, you need to find what value the Range("H2") code returns. You can use Debug.Print statements to track what values are assigned to the To property.
Second, I'd suggest using the Recipients.Add method instead of relying to the To property.
Set myItem = Application.CreateItem(olMailItem)
Set myRecipient = myItem.Recipients.Add("Eugene Astafiev")
myRecipient.Resolve()
Read more about that in the How To: Fill TO,CC and BCC fields in Outlook programmatically article.