White box appears that takes up half the bottom of the page

Site URL: https://back-it.squarespace.com/sports

As you can see above there is a white strip at the bottom of the site that I have not placed. And when you scroll to the bottom it even appears below the footer (making it look massive) and there is no option to remove this.

I have embedded a forum into my site too and when I click on something on the forum this happens:

Which effectively takes up 50% of the page (site header isn't included in screenshot) 

I would really appreciate some help in removing this so the  forum and site page can be seen properly.

Thanks

Is the same on the home page too even without the forum embedded.

Your site is private. Can you setup password & share url again? We can help easier