Update CoreELEC:
- Open Tools on the home menu
- Go down to Update tab and change "Automatic Updates" from auto to manual
- Click on "update channel" and select Coreelec 20
- Click on "Available Versions" and choose the highest version number (top option)
- Choose "YES" to confirm
- After the files download choose "YES" to reboot 
- The boot will stop at the CoreELEC logo screen. It will display text on the left side and reboot automatically
- Wait for the database migration and add-on migration process to finish

Fix TV Guide:
Open System > Addons > My Addons > PVR Clients > PVR IPTV Simple Client > Configuire > Edit "Migrated Add-on Config" [Enabled] > Click on OK at the right. Back out to the home menu > Power > Reboot. The guide should import after reboot.