Here are a few suggestions which might help.

(1) Try completely clearing your browser's cache before reloading your gallery's web page to see if this helps.
(2) Try viewing your gallery in different browsers (Chrome, Edge, Firefox, Internet Explorer, Opera, Safari) on your desktop computer to see if the problem is unique to a certain browser.
(3) If you have any browser extensions installed (like an ad blocker for example), try temporarily disabling them to see if this makes a difference.
(4) Try upgrading your gallery to the current version of Juicebox-Pro (v1.5.0). You can download the latest version using the link from your purchase email. Just swap your gallery's 'jbcore' folder for the one inside the Juicebox-Pro v1.5.0 zip package ('juicebox_pro_1.5.0/web/jbcore/'). Full instructions for downloading the latest version and upgrading existing galleries can be found on the Upgrading Juicebox support page.
(5) If you continue to experience difficulties, please post the URL to your gallery's web page so that I can take a look at the gallery for myself. I might see something that helps to determine the cause of your problem. Thank you.