If you are torquing the bolts to spec and applying loctite on the bolts than you are having an issue with the stem not being fully seated and while riding the jarring/bumps plus your weight is causing the stem to seat further on the steer stub.

You must be certain that the stem is all the way seated or you will continue to have the issue until it bottoms out on its own and you have re-torqued the bolts again.

I didn't recommend it or mention it but I generally remove the stem bolt and open the groove with a flat head, I then use a piece of wood under the fork drop outs and genitally hit the steam with a dead blow hammer (or Rubber mallet) to ensure it is seated as low as possible.