Nav bar and hamburger bar appear together starting from tablet view

I have a problem with my navigation. I recently purchased a Webflow template, and I am editing the navigation and trying to make it responsive, I notice once I click on template both hamburger menu and normal menu appear and when the hamburger menu is clicked nothing happens. I have noticed also It’s impossible to add any new navigation item next to “portfolio” without ruining it

my read only link
https://preview.webflow.com/preview/mariyams-ux-site?utm_medium=preview_link&utm_source=designer&utm_content=mariyams-ux-site&preview=74c3252358db7f756d4efa3f5b3f2fb6&workflow=preview

Here is my site Read-Only: LINK
(how to share your site Read-Only link)

You probably have made unintended changes on your template. But navigation on Webflow has a certain layout to maintain.

Your links should be within Nav Menu block. You can also see that when you click on add new link on menu settings.