SYNCING does not mean BACKING UP
Syncing on iCloud does not mean your files are backed up
You may think that if you've synced your planner on iCloud, you're files will be safe and sound. That's a huge confusion!
Syncing your documents on iCloud only allows you to view the notebooks across devices. However, if you mess-up a planner on your iPad it will automatically sync with iCloud so your planner will get messed up across devices with no possibility to undo the mistake.
Automated backup turned on? Don't 100% trust that either, please! The automated backups don't always work properly, and I only know this because I had to help a client recover her planner after the automated backup failed.
Here's what I suggest
For the safety of your files, please MANUALLY backup all your documents at least once a month (or even sooner) to a shared folder (like google drive or dropbox).
Keep your files safe!