Valve adjuster nuts
 

I had two of these come off at a recent DE. They were not replaced during the OH. What causes this besides not tightening them down a lot?

One suggestion was to use green Loctite (wicking).

How tight are you nipping them down. Once firm I go about1/16th turn. They are firm, but not pulling thread.
I think you should avoid loctite if possible, You are tweeking these fairly regular. Loctitite will bog up the thread and feel.
Alan