Looking at the second photo it would seem the bracket was loose. Note shiny ring around axle where the spacer washer goes. Also note lower right area of slot where the black smudge is, and black smudge on the bracket at the axle bolt/washer. First photos shows this a little, but very obvious in second photo.
I used a spacer washer that was a bit thinner than the bracket, and a large area washer under the bolt head and the nut. I had to loosen up the axle bolt to slide off the bracket but I did not have any cracking. With the front of the pant off, it is easy to loosen the nut a bit so the aft pant section can slide off after removing the socket head bolt and stand off.
Did you do anything for polishing/deburring the slot during the build?
Do you get the nose wheel off the ground as soon as you can on take off, and keep it off as long as you can when landing? Have you tried balancing the nose wheel assembly?