As you suggest, possible warpage or geometry issues. Maybe a past honer was also a bit heavy-handed in one stroke direction and also put too much pressure on the spine. In any case, were that my razor I would go back and make double sure that I am maxed out on my bevel setter. Assuming that's a synthetic water stone, adjust your stroke as necessary to ensure that you are pushing, and then undercutting "the wave" all the way across on both sides. Maybe some light work on your midrange 4K or whatever you use in the middle. I will also often strop after every stone with a blade that is giving me trouble like that to "seal the deal" at every level. I employ a number of tricks like that when honing a problem blade that can make all the difference.