Product category pages retain a transparent layer with MailChimp popup script

Hello:
I hope everyone is well.
Here is the basic info for my site:
https://wmalden.com
WordPress 4.9.6
PHP Version 7.1.19
MailChimp 4.2.3

The issue: when MailChimp popup script is inserted into header.php, it causes certain category pages (like the link listed above – product category pages) to retain a transparent layer. All other pages and individual product pages work fine, meaning the transparent layer does not show up on them.

Image of page without MailChimp script inserted: https://imgur.com/a/7nWJ6rx
Same page WITH MailChimp script active: https://imgur.com/a/rXQ0kse

All the pages of the site still work even those that have that transparent layer. Removing the script removes the issue, but of course then there is no more MailChimp popup to capture a visitor’s email address.

I have removed the script for now, so when you go on you will not be able to “see” the issue. I scoured this site and the MailChimp site and elsewhere but did not come across this issue.

Any help would be greatly appreciated. Thank you.