Well, I don't know much about Amazon fire products, so I'm naturally suspicious of them. :P But jokes aside, the last thing I'd inquire is whether you also replaced the old archive.rpa file with the new one. Because just installing the new apk is not enough when you update your game.
If that's not it either, then your issue would be above my paygrade and the best I can do is forward it to the gentleman responsible for building the Android version of Eternum.
Great! Guess I'm learning something new as well. Can you please send a screenshot of the error screen you were able to get? I could use it to infer what exactly the problem was. Make sure there's no personal info on there before you send it!
On another note, you shouldn't have random developer options toggled on all the time. I'd recommend you to first make screenshots of all the settings and then turn developer mode off, that should reset everything. And if you're in the mood for science, you can compare the default settings to your screenshots to figure out which setting did it.
