Bummer! I also use up all of my energy before the unlimited timer starts bc I know if I don't it'll be wasted. However even with doing so it still happens to me. For example today in the morning I did the last goal and after the timer ended I saw it was at 40 so I thought yay its back to normal. Then I collected from one pond and began to move stuff around and put things away. When I exited edit mode it said I had 16 energy. It sucks that it does this but at least I haven't experienced major rollbacks yet.