The cones can mismatch.
Expensive, but these are far stronger-
https://wheelsmfg.com/products/hub-parts/all-axles.html
I was constantly bending the rear on my "grocery getter" even though it's a Free Hub. (50 pounds in the rear baskets + my 250 at the time)
Found one of these on close out on another vendors site for about 1/2.
It's holding up.