I just tried it again, and remember this is my M3, not MS. All software up to date.
From the mobile app button bar (4 buttons of choice below the car icon on main app page), pressing the lock icon once from the mobile app unlocks only the drivers door. If I then immediately double tap the icon, it locks then unlocks, but only unlocks drivers door. Long pressing the lock icon only brings up the edit screen to move around the icons. So while in the Driver Door Unlock mode, there is no way to unlock the other doors from the app.
I then was thinking maybe I was using the wrong app screen/icon. So from the Controls screen of the app, the unlock button is in the center of the glass roof of the car image. Pressing this button works exactly the same as pressing the button as described in my previous paragraph, the only exception being that long pressing does not do anything. So still no way that I can find to unlock the other doors from the app.