The auto-rotate mode button may be missing from the Action Center on XPS 13 9365 and Latitude 13 7389 2-in-1 systems preventing the screen from automatically changing from portrait to landscape (or reverse) automatically.
Using Ctrl-Alt-> hot key combination to force the rotation works.
Reinstalling the sensor in Device Manager has no effect on the issue.
Reinstallation of the Intel Integrated Sensor Solution Driver will install the sensor drivers for the computer. Once you install this chipset package, all of the controls for screen rotation reappear. A pop up on the bottom right of the screen may appear as soon as the system is rotated. Click "Do not ask me again" in the popup. In Settings, turn off "Rotation Lock" to enable auto rotation. If Rotation Lock is enabled, the system will stay in Tablet Mode.