问VBA IF条件，其错误仅适用于第一个循环

EN

Sub graph()

    Dim cht As Chart, co As Object
    Dim i As Long
    Dim LastRow As Long, rngX As Range, rngY As Range
    Dim LastColumn As Long, wsMain As Worksheet, wsVol As Worksheet, wsData As Worksheet

    Set wsVol = ThisWorkbook.Worksheets("vol")
    Set wsData = ThisWorkbook.Worksheets("data")
    Set wsMain = ThisWorkbook.Worksheets("Main")
    
    For i = 2 To 500 Step 15 'loop in increments of 15
    
        If wsVol.Cells(2, i) = wsMain.Cells(3, 3) Then
            'define data ranges
            Set rngX = wsData.Range(wsData.Cells(6, i), wsData.Cells(Rows.Count, i).End(xlUp))
            Set rngY = rngX.Offset(0, 1)
            
            ClearWorksheetCharts wsMain 'remove any existing chart(s)
            With wsMain.Range("B26:F37")
                'add chartobject, setting position and size
                Set co = .Worksheet.Shapes.AddChart(xlLine, .Left, .Top, _
                                                     .Width, .Height)
            End With
            
            Set cht = co.Chart
            ClearChartSeries cht 'remove any "auto-added" series (if data was selected when chart was added)
            
            AddSeries cht, "25%", rngX, rngY
            AddSeries cht, "50%", rngX, rngY.Offset(0, 5)
            AddSeries cht, "25%", rngX, rngY.Offset(0, 10)
            
            cht.HasTitle = True
            cht.ChartTitle.Text = "1 month"

            With cht.Axes(xlCategory, xlPrimary)'X axis name
                .HasTitle = True 
                .AxisTitle.Characters.Text = "Time" 
            End With
            With cht.Axes(xlValue, xlPrimary)
                .HasTitle = True 
                .AxisTitle.Characters.Text = "Value"
            End With

         End If
    Next i
End Sub

'add a series and name it (factored out from main sub)
Sub AddSeries(cht As Chart, serName As String, serX, serY)
    With cht.SeriesCollection.NewSeries
        .Name = serName
        .XValues = serX
        .Values = serY
    End With
End Sub

'remove any existing series from a chart
Sub ClearChartSeries(cht As Chart)
    Do While cht.SeriesCollection.Count > 0
        cht.SeriesCollection(1).Delete
    Loop
End Sub

'Remove any chart objects from `ws`
Sub ClearWorksheetCharts(ws As Worksheet)
    Do While ws.ChartObjects.Count > 0
        ws.ChartObjects(1).Delete
    Loop
End Sub