On the first one, your database is corrupt. Go to the backup folder and look for the last good backup, then unzip it to the .kobo folder on your device. Then eject the device and reboot it for good measure.
If for some reason you don't have a backup (the log indicates you do), you can sign out and sign back into your Kobo account. This will fix the database but you'll lose the reading positions and such of all sideloaded books.
If you're on firmware 4.31, there's a known issue leading to more frequent db corruption and you'll want to upgrade to 4.32; see the
Kobo forum if you need help with that.