Sometimes when you're doing a yo between a knit and a purl, the yo gets kind of wrapped around the needle. When you go back on the other side, you have to sort of bring it down with your thumb around the needle in order to knit into the actual yo and the stitch after it.
I know this is clear as mud, but that's one explanation why it may not be working.
It could be, too, that the pattern doesn't really 'show up' for a while. Is it something that will need to be blocked aggresively, like lace?