I know that this is an ancient thread but I thought I would try picking it up again. I have do doubt that you gave excellent guidance but I was not confident at the time that I could implement your suggestions.
After re-visiting the thread with a clearer mind, I have restudied your remarks and want to try to resolve again. Let's use as an example once again, this page: https://gateslosangeles.com/gates-and-f … gates.html
Steven @ Juicebox mentioned on 2017-05-10 at 05:34:27
It seems strange that activating WP-Juicebox would prevent your web site from triggering its mobile mode.
Usually, factors such as the device (browser user agent), screen size and screen resolution will be taken into account when deciding whether to use desktop vs mobile mode but, from what you say, your theme's logic seems to also be considering page content. Maybe your theme's author can help determine why your mobile mode is not being used when WP-Juicebox is active. Other than loading the 'juicebox.js' JavaScript file and having a <script> tag with the gallery's embedding code, all that WP-Juicebox inserts into the web page is a <div> container for the gallery.
Checking out your website in Mobile Safari (iOS 10.3.1), the big difference between gallery pages and other pages seems to be that most gallery pages have large text at the top (above the header) such as "North Hollywood, Malibu, CA: Iron Gates in Los Angeles" in the link you provided. It seems to be this text that is not being resized appropriately. The rest of the web page seems to be responsive (the header fits the width of the web page and the navigation menu is hidden under the icon).
It might just be that your theme is not taking this text into account when resizing content for mobile devices.
I have found that the source of the text that you say is oversized comes from the site's General Settings > Site Title Can you confirm that is what you see as well or are you seeing something that seems to be from another source?