It seems that the Android app is saving after every single annotation. If you are working in DropBox, this burdens your connection a lot. It might be metered, and it might be slow. Also, a local backup might be an option, which is only saved back to Dropbox (or wherever) if the user decides to (or is prompted to).
Files should not be updated unless l do an explicit save or save as. Currently every file I open is "touched" whether I make any changes or not, which then forces a resync with my server. This is extremely annoying. Files should only be modified if I choose it.