If this fixes it for you can you mark the answer as solution. As to help the next guy. Thanks
You can un-install the secure folder to get the messages to stop. if you want to continue using secure folder, then you will have to tap on the notification, and login. this only has to be done once per startup, so is not as annoying as users on here seem to make it out to be, but if taking .5 seconds out of your day when restarting your device bothers you so much, follow these steps to permanently remove this feature:
Go into the secure folder.
Tap the 3 dot menu on the right
Go into Settings
Go into More Settings
Tap on Uninstall, and confirm the un-install.
After this is done, you will no longer have the notification upon startup (or a place to hide apps and pictures).
Here's why that is an unacceptable fix from Samsung. if you tap the notification, you are asked to LOG IN to your Secure folder, completely removing the thing that makes it Secure (the credential interface). If your home safe had an alarm that constantly went off WHILE IT WAS LOCKED, you'd be annoyed at that also.
Except that it ONLY comes up when you restart your phone. How many time have you re-started your home? Also, once you log in, you can lock your device, and unlock it, No message, and a locked secure folder. It literally took longer to complain about this feature than it would have to just log in and clear it.