Look Loosie! Identical picture, lol!
It looks to me like the hoof came into the ground like a sliding stop, ran into something that sheered the white line back from the wall. (well, that doesn't sound like a heel first landing) Nothing looks to be compromised...no trauma, so I'm not 100% on this theory. I'm thinking nothing that a well placed/maintained bevel wouldn't allow to heal it. Such a perfect half moon that indicates a direction, so I looked behind it and found the long red line that is mapped as clear as day on the top of the frog. I contoured in the bars, so you could realize what such tall/chunks they are. If you look at the long red line where it starts on the top of the left bar, it jams down to the groove at the heel, then splats over to the other side of the frog, where the high bar chunk on that side dictates and sends the force over between 10-12 o'clock. The mechanism should go equally up both sides of the hoof and break over equally from 10-2 o'clock. The breakover has been forced to only one side because of the bars dictating. There is tremendous torque at the toe and one side is not meant to take it all.
It's also possible that this direction of breakover alone has caused this weird separation. A force that is hard enough/coming down from a high bar, could jump the white line and cause the separation between wall and white line instead, pushing the white line back, instead of stretching it. For every yin, there is a yang and for every directional pull, there is a bite back.
The heels themselves are well balanced, just shortened them a bit and there's beautiful concavity going on at the toe...just those huge bars dictating a wonky use to this foot. A good balanced trim and bars re-shaped/lowered and stay on top of it. Bars are hard and have to be/should be worn out. When they get like this, its from not enough movement and/or the farrier not recognizing it and dealing with it. I see a really nice hoof right around the corner after a good relieving, balanced trim and no more worries at the toe.