For loop exiting prematurely

A “for loop” is exiting prematurely.

You can find the loop that is giving me troubles at the line(about half way down):
“For Row = DataRow To Ptr2FDc.count + DataRow”

The debugger gets as far as just before executing the line:
.Cells(Row, ElevationIDColumn).value = Ptr2FDc(Index).ID

The code exits immediately (without executing the above line of code) to the end of the workbook.

I checked the “for” variables. DataRow IS 2 and Ptr2FDc.count IS 20
Index has a valid number of 1

In the debugger I can see the PTR2FDc collection object and it does have an object in the collection at index 1. It is the correct object.

There is no error code

Public Sub PrintFDcollection(ByVal Wrkbk As Workbook, ByVal WrkSht4Printout As Worksheet, ByVal FieldDataCollection As MeasurementCollection)
    Dim Ptr2FDc As MeasurementCollection
    Dim LabelRow As Long
    Dim DataRow As Long
    Dim Row As Long
    Dim Index As Long
    Dim EndRowNum As Long
    Const ElevationIDColumn = 1
    Const X_CoordinateColumn = 2
    Const Y_CoordinateColumn = 3
    Const ElevationColumn = 4
    Const ElevationTypeColumn = 5
    
    With Wrkbk
        With WrkSht4Printout
'           Instantiate FieldDataCollection (copy of original) as a pointer
            Set Ptr2FDc = FieldDataCollection
        
'           store column labels in FieldDataCollection object
               LabelRow = 1
               .Cells(LabelRow, ElevationIDColumn).value = Ptr2FDc.IDColumnLabel
               .Cells(LabelRow, X_CoordinateColumn).value = Ptr2FDc.X_CoordinateColumnLabel
               .Cells(LabelRow, Y_CoordinateColumn).value = Ptr2FDc.Y_CoordinateColumnLabel
               .Cells(LabelRow, ElevationColumn).value = Ptr2FDc.ElevationColumnLabel
               .Cells(LabelRow, ElevationTypeColumn).value = Ptr2FDc.ElevationTypeColumnLabel
'
'           for as many Measurements exist in FieldData
            DataRow = 2
            EndRowNum = Ptr2FDc.count + DataRow
            For Row = DataRow To Ptr2FDc.count + DataRow
'              read MeasurementObj data into worksheet
                Index = Row - 1
               .Cells(Row, ElevationIDColumn).value = Ptr2FDc(Index).ID
               
               .Cells(Row, X_CoordinateColumn).value = Ptr2FDc(Index).Coordinates.X
               .Cells(Row, Y_CoordinateColumn).value = Ptr2FDc(Index).Coordinates.Y
               
               
               .Cells(Row, ElevationColumn).value = Ptr2FDc(Index).Elevation
               .Cells(Row, ElevationTypeColumn).value = Ptr2FDc(Index).ElevationType
             Next
        End With
    End With
End Sub