Strange floater hubs loosening

I have a old small style hubs that aren't made anymore by strange and they keep loosening up. Yes the lock ring is in there, yes I preload the bearing. Question is why is it doing it. Is the bearing getting ready to fail and losing it pre tension ? Are they just worn and need replaced. Thanks for the help

 

I've seen the same thing on ours and it is weird. It's only been on the right side and I've had it apart a number of times. I was expecting to find a smoking gun the first time I took it apart with the amount of play noticed but that was not the case. At this point I keep a close eye on it but haven't really found what the root issue is. Like most mysteries on these things it can probably be tied to tire shake. lol

Joad