Plugin shortcode breaks site footers

Dear Plugin Author,
I am attempting to install this plugin for a client who is a large international corporation, but it is currently unusable.

After inserting the shortcode into a page, and iframe shows up with th store locator, but the page footer will be missing (along with all the page scripts). This completely breaks the site, as you might imagine.

Without spending a bunch of time debugging it, I was able to narrow it down to the shortcode.

If I make my own iframe, instead of using the plugin shortcode, it works fine. Also, if I use the shortcode, but deliberately type a false value in, the shortcode error will display correctly (and the site works). I inspected your shortcode handling code, and noticed that it performs an ‘echo’ rather than returning a string, like it should, but other than that did not delve further into the problem.

Regards,
Leo De Bruyn

https://wordpress.org/plugins/bullseye-store-locator/