The "Find Blobs" operation lacks attachment for convexity or inertia parameters, and therefore uses the defaults from OpenCV (filterByInertia=true, minInertiaRatio=0.1f, maxInertiaRatio = MAX_FLOAT ; filterByConvexity = true; minConvexity = 0.95f; maxConvexity= MAX_FLOAT). As a result, the blob detector is biased for very smooth, closed blobs, making shapes like the attached very difficult to detect.

Exposing these options would make it easier to tune for oddly-shaped shapes.