The Dell Proximity Sensor application supports the auto-run feature only when the application stays in the system tray. Once you exit the Dell Proximity Sensor application, you have to re-launch the application and enable the feature manually.
The default setting of the Near and Away state in the Dell Proximity Sensor application is ON when you first boot the Latitude 7400 2-in-1. The default setting of the Near and Away state in the Dell Proximity Sensor application is OFF if the application is being closed and re-launched.
How to exit the Dell Proximity Sensor:
Figure 1: Click Quit to exit the Dell Proximity Sensor application
How to launch the Dell Proximity Sensor and enable the Proximity feature:
Figure 2: Click Change PC behavior… at the bottom of the Settings screen