It IS a cluster rib - the lower image; the upper image is a variation of the cluster rib which, I suspect, "clusters" a larger number of stitches. Cluster rib: multiple of 3 + 1 stitches; right side: P1, *K2,P1* repeat **
verso: K1 *YO, K2, Pyo over two just knitted and off right needle,K1* repeat **
This was particularly difficult to figure out as there are two cables spaced among three banks of this pattern stitch - and one of the cables had one stitch more increase than the other! But it works up very nicely (an easy stitch) to the correct bulk & gauge with two strands of worsted weight yarn on size 10 & 1/2 or 11 needles!