The messages aren't centered over the viewfinder in these rotated cases.  At least not if the viewfinder is smaller than the screen.  Also, the distance from the bottom of the screen to the notification is larger in the rotated cases.

When the camera is at 180 degrees, the text is upside down. Since all the icons rotate, shouldn't the text rotate, too?

If you hold the camera upside down, so the notifications are at the top of the screen and bring up the settings menu, change something, and then bring the menu right up again, you'll see the notification on top of the settings menu.  You either need to hide notifications when the menu is displayed or, (probably better) set the z-index so that the settings menu covers notifications if they overlap.