Sigh.  Flying this evening, I see that all my displayed data is now showing metric, despite having selected Imperial units previously (when I first got the drone).  So something has changed without me changing it...a "push" of an update from DJI to the app?  I even restored it to Imperial units, and the second flight on the next battery, it was back to metric.

Seriously?  This kind of nonsense is infuriating, AND worrying...what ELSE has changed that I don't know about?

Some settings do revert to default values with an update but otherwise they should stick as long as you have the Phantom connected when you make the changes.
Turn off auto updates and you won't get surprises.