Various tips in [this thread on WPCentral](http://forums.wpcentral.com/nokia-lumia-920/211575-find-my-phone-shows-off-settings-menu-but-appears.html) eventually got me set.

I'm not sure if all of these steps are required or not, but they were for me:

 - Turn off **find my phone**
 - Force a backup to the cloud in **settings > backup > app list+settings**
 - Delete all your phones on windowsphone.com. It will warn you that your phone will no longer be able to connect to your account, ever, unless you factory reset it.
 - Factory reset phone. I imported my settings from the cloud and waited.
 - Once it was up and running, I turned **find my phone** back on.

My settings look normal now (though I can't remember if the on/off switch should be there):
![settings > system][1]![settings > system > find my phone][2]


  [1]: http://i.stack.imgur.com/lM62X.png
  [2]: http://i.stack.imgur.com/YX0rR.png