I acquired a new iPhone yesterday, and initialised it with a restored backup from my old phone.
When SkyDemon loaded, it did so without any charts, but it did know that I'd been logged in using my user account on the old device. After clicking "Agree", because there are no charts loaded, the app goes straight into the chart selection page - however, because this is a new device that hasn't been logged in before, it brings up the "This device is no longer logged in to the SkyDemon system" message, which helpfully directed one to "open the setup menu... log back in again".  Unfortunately, you gets stuck in a loop such that when it can't load a chart, it throws you back to the "Agree" welcome screen - you can't get into the main program to get to the Setup menu.

The only option, I figured out, was to delete the App and reinstall, forcing it to forget who was logged in in the first place.

Thanks, that is a niche but important bug. You did just the right thing to make it work again, but we will add some behaviour to detect this circumstance and present the log in window again.