Thanks for the video and additional information.
Unfortunately, as the problem happens only in a browser that I do not have access to (and, therefore, I cannot replicate the problem myself), I'm going to need your help to troubleshoot further.
Here's a test gallery using exactly the same configuration options that your gallery uses except for the value of emailAddress . (I've removed your email address from the test gallery.)
The test gallery even uses a baseUrl as your gallery does (with the same folder name) and also has the same dimensions and background color.
Also, both galleries (yours and mine) use the same version of Juicebox-Pro (v1.5.1).
The only two differences between your own gallery and mine should be:
(1) the images in the galleries
(2) the web server that the galleries are hosted on
Test Gallery: [Link removed.]
Please take a look at this test gallery in Safari 11.1.1 to see if you still see the problem.
This might help to narrow down the root of the problem and eliminate certain factors.
Also, are you able to update to the latest version of Safari (11.1.2) just in case the problem is somehow unique to Safari 11.1.1?
If this turns out to be a browser-specific bug in Juicebox-Pro (which it looks like it might be), I may not be able to solve your problem immediately but, once I've gathered as much information as possible, I can at least contact the developers who will investigate further.
Thank you.