Imgproc.findContours not returning all contours [closed]

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Small issue again. I'm using the imgproc.findContours in Java:

Imgproc.findContours(imgContours, points, hierarchy, Imgproc.RETR_EXTERNAL, Imgproc.CHAIN_APPROX_NONE);

When I use the following canny'ed image:

I get following contours:

Can someone please explain why the findContours is behaving like this? There's almost no difference in the Canny image between the upper and lower row and the lower contours are fully enclosed, but still it's not returning the contours.. Thanks!

Full code:

private List<Rect> getBoundingBoxes(Mat image, Mat originalImage) {
        Mat imgContours = new Mat(image.rows(), image.cols(), image.type());
        image.copyTo(imgContours);
        Mat imgEdgesFound = originalImage.clone();

        List<MatOfPoint> points = new ArrayList<>();
        Mat hierarchy = new Mat();
        Imgproc.findContours(imgContours, points, hierarchy, Imgproc.RETR_EXTERNAL, Imgproc.CHAIN_APPROX_NONE);
        List<Rect> boundingBoxes = new ArrayList<>();

        if (hierarchy.size().height > 0 && hierarchy.size().width > 0) {
            for (int idx = 0; idx >= 0; idx = (int) hierarchy.get(0, idx)[0]) {
                Rect bounds = Imgproc.boundingRect(points.get(idx));
                Imgproc.drawContours(imgEdgesFound, points, idx, new Scalar(250, 0, 0));
                if (bounds.height > Configuration.PictureProcessor.getDigitMinimumHeight() &&
                        bounds.height < Configuration.PictureProcessor.getDigitMaximumHeight() &&
                        bounds.width > Configuration.PictureProcessor.getDigitMinimumWidth() &&
                        bounds.width < bounds.height) {
                    boundingBoxes.add(bounds);
                }
            }
        }

        Collections.sort(boundingBoxes, new BoundingBoxesComparator());

        if (Configuration.PictureProcessor.isDebug()) {
            Imgcodecs.imwrite("output/debug/edgesfound.png", imgEdgesFound);
            logger.info("Number of boundingboxes found: " + boundingBoxes.size());
        }

        return boundingBoxes;
    }

Update: RETR_LIST seems to work, but now I get a lot of duplicates..