Ohhhh I found my mistake
Frogging back the 6th time I realized that I had not gone far enough.
I had not frogged back to the original button hole. If I had I would have seen that I had failed to pickup the YO on the return row. Which would have, of course, created that missing stitch from the k2tog. Ah ha!!
Gee that was silly!! At least I read the pattern correctly!