MailChimp provides code that you can embed in your website to create a subscriber popup form. After adding this code, you may find that Beaver Builder no longer works.
The solution is to be sure to put the popup code into the footer area of your site. If you're using Beaver Builder Theme, add it to Customize > Code > Footer code.
If you put the MailChimp popup code into the content area using a Beaver Builder module, the best workaround is to open the page for editing in WordPress and revert to the last revision of the page, then add the code to the footer section of your site.