Can the user who is updating their field see the field? If not it will get reset to empty if they don't meet the condition. You can turn off value resetting globally within CB Conditional > Parameters, but currently it can't be adjusted on a per field basis yet.
(i would like to have a field for a user reserved only for superusers or moderator)
If you want a field to be editable by moderators only, even if editing another users profile, you should use CB Privacy for that instead since it conditions off the viewing user and not displayed.