CPanel made an announcement this month that it will discontinue support for the Paper Lantern theme. Luckily it's easy to upgrade to the new Jupiter theme server wide.
To migrate all accounts to Jupiter, you can navigate to WHM » Multi Account Functions » Modify/Upgrade Multiple Accounts
You can also do it via the command line with this code:
/usr/local/cpanel/scripts/modify_accounts --theme=jupiter --all-users
