As Exup pointed out, possible cause might be something else than clear traditional corrosion spot.
-maint error
-previously damaged threads on axle/nut
-bearing damage
-traditional corrosion on axle
-corrosion/heat damage possible previuous bearing failure
-with heat damage, there is possibility to have problems with axle plating cadmium. Turns problematic with axle steel.
-manufacturing error on overhaul
-hard landing earlier, undetected failure
Time will tell.