Problems:
-Ads start playing randomly.
-UI overlay issue; when you click on an option to spend your energy on the entire screen becomes transparent so you can see the option being deployed the problem with this is that the option description (how much energy it produces) can only be viewed by clicking it so the transparency makes it hard to read.
-From my understanding you can only collect 1 hr worth of energy after you close the app.
Overall it's a good game and, while I haven't completed it, the rest of the game isn't stuck behind a paywall, you do have to watch a video to go to the next chapter tho.