Short time solution:
I've started making copys of my game via copying the file to my computer. If it crashes just delete the old file and replace it with your backup.
Still it's annoying that this issue happens and hasn't been delt with.
That's how the cookie crumbles when it's a game that doesn't have to be always online.
It cuts costs to not have to backup saves on their own servers. Which is the difference between ads and no ads.
Any backup operation is just as fallible as the original save operation. Especially since it would be stored locally on the device.
The most that could be done is to stagger the backup operation to after the save has completed and the save is verified to be correct.
Either way though if your device is wrecked both the backup and the save are wrecked as well. No way around that unless you want server side storage and ads to support the cost of storing your data.
Addendum:
If the app had a feature in the help menu and asked for permissions to access your google drive it could save there provided you had the space.
Dunno if apple has a similar feature.