The White Flash on screen that you have described is the Night Vision Mode.
When in AUTO mode (and at night), there is a brief white flash on the screen and then the night vision starts on the Parent Unit.
Approx. every 20 seconds, there is a white flash again on the screen, because the Infrared lights must verify if the night vision mode is still needed.
This is because on AUTO mode the Infrared lights will be activated only if there is low visibility.
When in NIGHT VISION ON mode, the Infrared lights will be automatically switched on and will remain activated.
The first white flash will appear briefly when the Parent Unit is switched to this mode, but this white flash won’t happen after that.