Since row 5 also has Dec along with ssk and k2tog, maybe it's another type of decrease like a double decrease. Looking at the repeat in row 5 there's 4 YOs, and with 2 single decs, the other would be a double dec so you offset the YOs. Row 7 has 2 yo and no other decs, so it should be a double one. Look to see if the pattern eplains it because it could be sl 1, k2tog, psso, sl 2, k1 psso, k3tog or sssk.
sue- knitting heretic