Sorry for the late reply. It looks like your query somehow slipped through the net.
WP-Juicebox (the Juicebox plugin for WordPress) embeds galleries in WordPress web pages using the regular embedding method documented here.
All that is loaded into the web page is the 'juicebox.js' file (and the 'theme.css' file dynamically afterwards).
All the CSS in the 'theme.css' file should target the gallery only. As far as I am aware, there are no CSS rules that should affect any other elements on your web page.
There may somehow be a JavaScript conflict but all it seems strange that the problem has happened only with your new theme.
It would certainly be worth making sure that you are using the latest versions of WordPress (v4.6.1) and WP-Juicebox (v1.5.0) (and WP DFP if you are using it) to see if this helps. You can download the latest version of WP-Juicebox from the plugin's support page here. Be sure to upgrade the plugin using your Juicebox-Pro v1.5.0 files. (You can download Juicebox-Pro v1.5.0 using the link from your purchase email. Full instructions can be found here.)
Try viewing your web page in different browsers (Chrome, Edge, Firefox, Internet Explorer, Opera, Safari) to see if the problem is unique to a certain browser. Also, if you have any browser extensions installed, try temporarily disabling them to see if this makes a difference.
I'm not sure it will help but this is the only forum thread I can find in the WP DFP support section which seems similar (if not identical) to your problem. I just thought I would point it out in case it helps.
WP DFP Loads Twice (Ads Flicker) - https://wordpress.org/support/topic/wp- … s-flicker/