This anomaly applies to IC Rev. Engineering A, build codes QIAA-AA0.
In System OFF mode, the device will not wake up when VBUS supply is connected.
Always.
The device remains is System OFF mode.
External circuitry can be used to translate VBUS voltage levels to GPIO voltage levels that can be used to trigger a GPIO DETECT signal (configured using the GPIOTE peripheral) to wake from System OFF.