Sign up page is reloading and missing the info already added after clicking on the template

I’m using New Blog Templates to create a default template on my site and I have added a form via a mu-plugin in order to allow to sign up for a new site from the front-end.

And when trying to sign up a new site from the form, after adding the site details on it, once I click on the template image the sign up page is reloaded to itself but the form appears empty and no site is created.