Hi and Welcome. Here's the link
to the pattern stitch so others can find it too.
This stitch pattern has a different number of stitches on each row. The repeat - yo, k1, yo, k3, yo, k1, yo, ssk, k9, k2-tog - has 4 YOs but only 2 decs so you gain 2 stitches there. The beg of row has a dec and no inc, and the end stitches add 4 YOs and only 1 decrease. So at the end of the row you'll have added sts, but row 2 has the decs that make up for it.
It's counted a bit odd, but try reading it as the last repeat of the repeats isn't done the same as the other ones. The YOs don't use a stitch, so you do use 18 sts in the repeat, 7 sts before it and last repeat ends with 'k2tog, k5' instead of 'ssk, k9.