.Hyperlinks.Add Error Midway through Routine

You could try inserting the HYPERLINK function instead. You won't get a screen tip, though.

    cAddress = g_cSheet.Cells(cRow, cCol).Address
    anchorCol = FindColumn(QCSheet, QCCol04) 'anchor column'
    Set aAddress = QCSheet.Cells(qcLastRow + 1, anchorCol)
    saAddress = "'" & g_cSheet.Name & "'!" & g_cSheet.Cells(cRow, cCol).Address
    stText = "Go to " & cAddress & " in the '" & g_cSheet.Name & "' sheet."
    ttDisplay = g_cSheet.Name & " " & Replace(cAddress, "$", "")
    
    With QCSheet
        .Range(aAddress).Formula = "=HYPERLINK(" & saAddress & ", " & ttDisplay & ")"
    End With

Thank you that will solve the interim problem. As these issues get resolved over time, the limitation may be hit initially, but they quickly resolve to well below that 66,530 limitation.

While this did identify the issue, creating an if then (if number reached then do something different), the alternative workaround proved to not work either. After multiple testing, it seems the concept would work, but the code

With QCSheet
        .Range(aAddress).Formula = "=HYPERLINK(" & saAddress & ", " & ttDisplay & ")"
End With

does not work. I am at loss as to what part of it does not work. Again tested for over a dozen runs. The fields are good, but I still get a 1004 error.

I appreciate any advise on how to resolve the problem. I think I have been staring at the problem for too long! Hopefully, fresh eyes might point out a solution.

It is mapping to the right address for the .range(aaddress).formula portion ==> '[Testing.xlsx]QC Results'!$D$65535
It appears to be getting the right information in the formula ==> =HYPERLINK('Data Consolidated'!$G$2, Data Consolidated G2)

Ok. After a few hours of looking. I found bits and pieces that led to a solution. I am not sure if there is a more effective way, but here is a final solution that works.

Thanks to 6stringjazzer the primary problem of a limitation within Excel was identified. The possible workaround proposed by 6stringjazzer also got me on the right path for a viable solution.

    cAddress = g_cSheet.Cells(cRow, cCol).Address
    anchorCol = FindColumn(QCSheet, QCCol04) 'anchor column
    Set aAddress = QCSheet.Cells(qcLastRow + 1, anchorCol)
    saAddress = "'" & g_cSheet.Name & "'!" & g_cSheet.Cells(cRow, cCol).Address
    stText = "Go to " & cAddress & " in the '" & g_cSheet.Name & "' sheet."
    ttDisplay = g_cSheet.Name & " " & Replace(cAddress, "$", "")
    
    If qcLastRow + 1 < 65531
        With QCSheet
            .Hyperlinks.Add _
                anchor:=aAddress, _
                Address:="", _
                SubAddress:=saAddress, _
                ScreenTip:=stText, _
                TextToDisplay:=ttDisplay
        End With
    Else
         With aAddress
            .Formula = "=HYPERLINK(" & Chr(34) & "#" & saAddress & Chr(34) & ", " & Chr(34) & ttDisplay & Chr(34) & ")"
        End With
    End If