Apps occasionally have to reload from internet. Major problem

Every once in a while, usually at the WORST TIME, an app reloads on my iPad(s) - I suspect re-downloading from the APP store although sometimes preloaded apps do the same thing. The reloads are via the internet. This has happened with Mail, Files, the installed browser, Chrome and worst of all OnSong - a professional musicians database of songs. That latter left me without my songlists and chord charts DURING A GIG where I didn't have internet access!!!

WHY is this happening and how can I make it STOP?

Maybe they're "upgrading" but I want to control when that happens and not be left in the lurch when I NEED an app or don't have an internet connection.