What userid are you trying to login with that does not see the changes? What user roles do you have in your project? Have you defined different home pages for different user roles?
Any info you can provide will help with troubleshooting.
Now that I look more closely, I suspect it is a problem with the Language configuration in your project. Check the default language (in Studio Pro, go to Language | Language Settings. Seems like a mismatch between your default language and browser settings. So when you turn off security, you are getting Dutch and when you turn it on, you are getting English (which is boilerplate if you have changed it). Also, you may need to check the language for the users you have created.