Is it a misuse from my side or it's impossible to know.
(Probably I didn't screw it till the end before it was broken or maybe I applied to much force, when closing it.)
P.S. It's prequel to this question Can I use rear (thru) axle with crack for a few rides, before getting a new one?, but not related to it.
I was asked for a full axle picture:
I was wrong so I decided to rewrite my answer.
I went to look at the bike in my shed that has a similar axle. This axle type works so that the axle is tightened by opening the lever completely and using it as a handle to screw the axle in. The slot in the axle head is not made of material that is strong enough to handle the torque required to fasten a bicycle wheel, so it starts to deform immediately.
After that, the lever is tightened and the cam built into the lever pushes the silver coloured cone into the axle, spreading the axle ends outwards. The outward pressure prevents the axle from becoming loose. The cam seems like it would operate like a QR axle cam, because it looks just like one, but this is a lie and it does not add any clamping load to the axle.
The small hole in the axle slot tries to act as a stress relief point, but it does not work if the axle is too loose. Or maybe it doesn't work at all. Maybe someone has closed the cam while the axle was not in the bike, making it expand so far that a crack started from the hole and eventually gave in completely.
Sadly, this is only the second stupidest through axle design I have seen on a Kona bicycle. It should be replaced with an axle that is tightened with an allen wrench.
