QWT Plot does not update

[codeaway]

Greetings,

Have QWT 6.1.5, QT 5.15.0 and MSVC2019, trying to do a plot:

void MainWindow::setupGraph()
{
	QColor c(Qt::black);
	c.setAlpha(140);

	QPalette pal;
	pal.setColor(QPalette::Window, c);

	ui->qwtPlot->setTitle("Monitor");
	ui->qwtPlot->setAxisTitle(QwtPlot::xBottom, "Sec");
	ui->qwtPlot->setAxisScale(QwtPlot::xBottom, 0, 100, 10);
	ui->qwtPlot->setAxisTitle(QwtPlot::yLeft, "mV");		// Y axis title
	ui->qwtPlot->setAxisScale(QwtPlot::yLeft, 0, 100, 10);
	ui->qwtPlot->setAttribute(Qt::WA_TranslucentBackground);	// background colour
	ui->qwtPlot->setPalette(pal);


	QwtPlotGrid *grid = new QwtPlotGrid();
	grid->setMajorPen(QPen(Qt::darkGray, 0, Qt::DotLine));		// grid is black dotted
	grid->attach(ui->qwtPlot);

	curve = new QwtPlotCurve;
	curve->setPen(QPen(Qt::green));					// plot is green
	curve->setRenderHint(QwtPlotItem::RenderAntialiased, true);	// plot anti aliased
	curve->attach(ui->qwtPlot);
}

void MainWindow::updateGraph()
{
	int i = 0;

	while (1) {
		sec[i] = seconds;
		qDebug() << "Sec:" << sec[i] << "," << "Ch0:" << ch[i];
		seconds++;
		i++;
		if (i == 5)
			break;
	}

	curve->setSamples((double *) sec, (double *) ch, 5);
	curve->attach(ui->qwtPlot);
	ui->qwtPlot->replot();
}

From my MainWindow, I do setupGraph();
and as I get data, I do an updateGraph();

The qDebug() debug log messages I can see:

Sec: 0 , Ch0: 21
Sec: 1 , Ch0: 24
Sec: 2 , Ch0: 20
Sec: 3 , Ch0: 23
Sec: 4 , Ch0: 22
Sec: 5 , Ch0: 21
Sec: 6 , Ch0: 21
....

But the Graph does not seem to plot any points ?
I can see that the Plot has setup correctly with the set values in setupGraph()

Am I missing something in here ?

Thanks,