It also appears whenever your regen changes. That means if your battery starts cold with limited regen, and your energy gauge is not present, it will appear. Then when your battery warms up and you regain more regen, the energy gauge will reappear. It will show itself again when you have full regen and no dotted lines. I thought it was a problem at first, but it is just bringing your attention to the level of regen you currently have and that it is either changing or not 100%.