How have I got Two identical iCloud accounts? When I look in Internet Accounts, I have two identical iCloud accounts. How can I get rid of 1 of them?
You can delete both - it will let you know if any data needs to sync up and then you can sign in again.

Sometimes the system loses track of a preference, so I recommend a back up of your local data and then perhaps restarting / disk check to be sure the storage is healthy before adding the account and re-syncing data.