"No spinners" gets super annoying when devices go to sleep or internet is spotty. Am I looking at the latest data? Is it safe to turn off my phone / exit the app, or is still uploading? I dunno, let's give it a minute just in case...

This is easily solvable with any sort of sync button. Granted, you may in fact have to at least in name break "no spinners" (but to my understanding not in practice), and shove one in the top right corner of your app when syncing / uploading / downloading is occuring, but obviously it's better than just sitting there and waiting.