You know what? I just checked it and Google Drive backed up some time last night. I guess it just does it when it wants to. So, Google Drive has accomplished a backup now. I'm not sure when it'll backup/sync in the future. I'll have to look at the settings again.
But Samsung Cloud just doesn't work. It'll go down the list of things I'm trying to back up and it'll say "Can't back up data" for every single one of them. When I first click on Settings>Cloud and Accounts>Samsung Cloud>Backup Settings it says "No Data to Back up" when there is obviously new data. For most of the apps in the list it actually says that it backed them up on 5/2/17, so I guess it actually did something once, but it's been a while. When I click "Back Up Now" is when it just goes down the list and says "Can't Back Up Data"
Maybe this is just the way this works, but Auto Back Up is supposed to happen every 24 hours. The problem might be that I rarely connect to WiFi. But, I also told it not to worry about that, just back it up.
Maybe this will help. I get an error messages that say "Couldn't back up data - An error has occurred (305)" and "Couldn't sync data - An error has occurred (305)"