Hub nut backs itself loose

2000 toyota driverside automatic 4 cylinder. About 30,000 miles agao kid hit curb so i replaced the axel with aftermarket no problems until reciently the hub nut backed itself off to the cotter pin. i re- tightened and it did it again then i re tightened and added red lock tight if it does it again, replace the axle again? The alignment is fine no other issues… Would not of known it was loose but the rotor was dragging against the dust shiled when turn left…

Assuming the nut is tightened to the proper torque it’s possible that the aftermarket axle (reman?) could have a history of someone in the past really whaling on the nut with an air wrench.
This can cause the threads in the nut and/or on the axle to pull and when this happens the nut may never stay tight.

Careful examination of the threads with a magnifying glass may be necessary to determine if the threads are pulled or not and Loc Tite should not be needed on something like this.

Didn’t your repair manual tell you to replace the axel nut?

Did you reinstall the washer? Is the axle nut a castle nuts, like this:

Does the castle nut engage the cotter pin? If not, that’s your problem. The castle nut MUST engage the cotter pin to prevent it from backing off. The washer is designed to space the nut to the hole for the cotter pin and spread the load from the nut across the spindle. Also, the nut MUST be torqued to the proper tension. Did you torque it down to the proper torque spec?

Also, the axle and nut not only fasten the axle to the hub, but fastens the hub the the steering knuckle. If you cannot get this assembly attached correctly, you will damage the wheel bearings, as the hub will be allowed to move in ways not designed.