HP has pushed out version 126.96.36.199 of their Double Tap app for the Elite x3 that enables both double-tap to wake and the ability to toggle the display by lowering or raising the device.
The update does not have a specific changelog, but the overall performance is getting better from our experience.
HP Double Tap app found under Settings > Extras lets users configure the duration and timing of the double-tap events. The feature does not work on display technology but rather the accelerometer making it a little more finicky than usual.
Additionally, the enable double-tap also enables a 'raise to wake' as well as the reverse feature – 'lower to lock.' Raise to wake works by just picking up the Elite x3 and having the display turn on to show notifications. Likewise, placing the phone down on a flat table turns off the screen thereby locking the phone automatically. The latter is likely a security feature so that an employee does not accidentally leave their phone on and unlocked if unattended.