Thanks for this advice KKK, I've found other apps that are saying the same thing, that saved data in apps may be lost and to take steps to avoid this before the upgrade.
We've also seen some apps crashing already with the latest updates in preparation for the new OS.
Looks like we may be in for a teething period with the new upgrade with some apps.
I'll just mention it here also, Genius in the App Store will also be replaced by a feature called Near Me. It will be a useful feature for those of us who travel frequently.