Apparently it is something to do with the iPhone backup to the cloud, the app becomes unavailable as it clears out cache to make the app backup as efficient as possible.
What frustrates me is…
1) why does the phone not do this when I’m asleep? It could know when I’m asleep due to usage habits.
2) there does not seem to be a ‘stop cleaning’ option to use the app – imagine if the ‘phone’ app would not allow a 999 call because it was ‘cleaning’.
3) it should be better than this, this is not a Microsoft product.