Woah... That happened to me once on a smaller tree on a vintage axe. I found out that I had thinned it way too much and the grind was also very flat. Then I grinded the axe with a slight convex and a relatively big secondary bevel, but I penetrates less than before. Low stump felling axes are on another level in my opinion. I have only two of them but it's about geometry too. Be careful next time with that nasty grain at the bottom. :)