Footer doesn't go down with read more (blocks content)

Hi,
I’m making a web site for a company and I want to use a “read more” functionality in a page (not a post). This works with the plugin “WP show more” or “read more without refresh for WordPress”, except the footer won’t go down to the bottom of the page when I click on “read more”, which makes the contact button disappear in the footer.

I use the “Tesseract” theme, you can see an example of the problem here.

Does anyone know how to fix this?

Thanks in advance!