How to deal with multi page app and loading phase

Hi there, I’m building an app with login and logout. I saw some implementations where these two options are always visibile in the menu but in my case I want a specific page for the login. So after the login I call from radio buttons the page which the user requires. The problem is that in the loading phase I saw in trasparency all my blocks moving around the page. ( for example a form block in the right which moves to the left ). What can I do in order to fix element in the loading phase?