I have had trouble with my account for several months. Half the time it won't even let me into my account. When I go back to the previous page, it's totally different. It keeps showing old account settings that have been updated. Just a complete mess. And I can not get into my cloud or backup my DATA on my samsung account. I have deleted cache and DATA several times. It always starts doing the same thing as soon as it takes my password.
Have you checked under Settings > Accounts and Backup> Accounts and clicked your Samsung Account to make sure there isnt anything under the "Services that can Sign in" or "Services that can access your info" that may be causing a conflict. It sounds like there may be another trusted device that may be conflicting wity your samsung account. I would sign in to see if there is a way to untrust devices or clear unneeded devices to see if that fixes the issue..If not, it sounds like maybe a server issue on Samsung's end..you may want to chat or give them a call to see if they have any suggestions for your account.