Version 1.51
PHP Version: 5.5.38 (Zend: 2.5.0)
Website: tubularwiremeshribbon . com

After a nameserver change to facilitate transfer to a new host I'm seeing some odd behavior, both in the Zen back-end and on the site. I'm not quite sure how to deal with it and am hoping for some guidance here.

In the back-end when I attempt to make changes, updates, etc., I receive the following pop-up message:
Security Warning: The information you have entered on this page will be sent over an insecure connection and could be read by a third party.

Are you sure you want to send this information?
And then whatever changes I've attempted do not stick.

FYI: The site is encrypted using Let's Encrypt.

In the front-end, adding items to the shopping cart from the product page seems fine but if I attempt to do so from a page that lists all the items in that category, I receive the same error message as mentioned above. For example, please visit this page and attempt to "Add Selected Items To Cart".

Any thoughts? Thank you!