@DubbleAitch: I'm sorry to hear that you have encountered this issue with your Secure Folder. Please can you attempt the steps below, to see if you're able to resolve the issue?
1) Settings > Apps > Samsung Account > More options(...) > Tap 'Uninstall update' (Samsung Account v14.0.00.11)
2) (In case of reset Password needed) Settings > Tap and sign in 'Samsung Account' on the top > Run 'Secure Folder' > Mistype Password > tap 'Forgot password' > Tap 'Reset' on the reset Password popup > Enter New Password.
Let me know how you get on.