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).