Narrow staples (gun). Yes, usually have to lightly persuade them with a small hammer to finish the job with the modern pallets.
BUT, i also rarely bother with synthetic grips, I definitely staple the leather.
LIkely a shank. If it occurs again in the same spot, maybe not.
I sometimes mark a location (of a break at the frame) with a sharpie. In the event it happens again in the same spot
you will at least have a direction to go in regarding the cause.
I'd suggest putting on the extra nuts as those are for locking the wheels in place at different lengths.
Useful on uneven floors. Perhaps you don't need them, but i do. Additionally, they will (perhaps) unscrew
on their own, so those extra nuts (when tightened against the "foot" will lock them...