First of all, let’s make sure that you are looking in the right place. When you view a login item in the Desktop app, there will be some metadata (timestamps, etc.) at the bottom. If there is a password history, you will see the text “Password history” followed by a number, at the very bottom. You need to click on that number to see the old passwords.
If you are looking in the right place but are not seeing any password history, then you might possibly have a sync issue. In that case, log out completely (File > Log out), and log back in.