Getting a series trend line equation to a shape text box

Question

I'm attempting to get the trend line equation from the first series in my chart to a shape text box placed elsewhere on the worksheet - however, I can only get the textbox to populate correctly when I'm stepping through the code line by line - during run-time it has no effect:

For Each chtObj In ActiveSheet.ChartObjects

    Set cht = chtObj.Chart

    For Each srs In chtObj.Chart.SeriesCollection
        srs.Trendlines(1).DisplayEquation = True 'Display the labels to get the value
        ThisWorkbook.Worksheets("MyDataSheet").Shapes(slopetextboxes(k)).TextFrame.Characters.Text = srs.Trendlines(1).DataLabel.Text
        srs.Trendlines(1).DisplayEquation = False 'Turn it back off
        Exit For
    Next srs

    k = k + 1 ' for the slope textboxes

Next chtObj

Note that slopetextboxes is an array containing the names of ~6 shape text boxes.

As far as I know there's no way to get the trend line data label without stopping to display it. I've tried storing it in a string first, DoEvents, and turning Application.ScreenUpdating back on, all to no avail. I'm stumped here.

EDIT: It appears that by placing DoEvents after .DisplayEquation = True I'm able to have some of my shapes populate correctly, but not all. Still appears to be some kind of run-time issue.

BOUNTY EDIT: I've moved ahead to grab the slopes with a formula ran into the data itself, but I still don't understand why I can't grab the chart's .DataLabel.Text during run-time. I can grab it when stepping through, not during run-time. It appears to just take the PREVIOUS series slope and place it in the shape (or a cell, it doesn't even matter where the destination is). DoEvents placed in different spots yields different outcomes, so something must be going on.

Answer 1

Updated with better understanding of the bug. This works for me in excel 2016 with multiple changes to the source data (and therefore the slope)

I tried myChart.refresh - didnt work. I tried deleting and then re-adding the entire trendline, also didnt work.

This works for everything but the first case. First case needs to be hit twice. Same as for .select

If you try and delete trendline even after assigning its text to textbox, this wont work

Option Explicit
Sub main()
Dim ws                                  As Worksheet
Dim txtbox                              As OLEObject
Dim chartObject                         As chartObject
Dim myChart                             As chart
Dim myChartSeriesCol                    As SeriesCollection
Dim myChartSeries                       As Series
Dim myChartTrendLines                   As Trendlines
Dim myTrendLine                         As Trendline

    Set ws = Sheets("MyDataSheet")
    Set txtbox = ws.OLEObjects("TextBox1")

    For Each chartObject In ws.ChartObjects
        Set myChart = chartObject.chart
        Set myChartSeriesCol = myChart.SeriesCollection
        Set myChartSeries = myChartSeriesCol(1)
        Set myChartTrendLines = myChartSeries.Trendlines

        With myChartTrendLines
            If .Count = 0 Then
                .Add
            End If
        End With

        Set myTrendLine = myChartTrendLines.Item(1)

        With myTrendLine
            .DisplayEquation = True
            txtbox.Object.Text = .DataLabel.Text
        End With
     Next chartObject
End Sub