Hello, I builded website in odoo using graphical editor. Next i wanted to add login form.

<form class="oe_login_form" role="form" t-attf-action="/web/login{{ '?debug' if debug else '' }}" method="post" onsubmit="this.action = this.action + location.hash"> 
INPUTS
</form>
Then I can not edit site anymore by graphical editor. I can run edit, edit content(text) but can not delete or insert blocks. 
The same thing happens when I add 

<t t-if="website.user_id == user_id">

Which should check if user is logged or not and display suitable content. 

How should I insert that code? 

Odoo 12 community