macOS Safari expert needed to find cause of iframe-related problem

We are finishing up a new web site ([login to view URL]) and have found a bug that shows only on macOS Safari. The team does not currently have Mac experts, so I'm hoping the Freelancer community can help. The site is built around the YouTube video player, and includes an iframe that shows external sites. The problem can be reproduced as follows: Using Mac Safari and the mouse/trackpad set up to use the 'Swipe between pages' shortcut. 1] Load [login to view URL] 2] Stop the video playing 3] Click on the 'Gustav Holst' link - this loads the Wikipedia page into the iframe. 4] Click the first link in the article: "Holst (surname)" - this article appears. 5] Use the mouse, and swipe left-to-right to trigger 'Swipe between pages' Result: you will be taken back to the article on Gustav Holst but the entire site is now unresponsive. It is likely this problem is related to the presence of the iframe rather than Wikipedia because it occurs with other sites too. The problem also appears to be limited to recent versions of macOS and Safari - on El Capitan system with Safari 11.1.2 the problem does not occur. This project is initially just to find the cause of the problem, but could be extended to include the fix - for a larger fee of course. Please include the keyword 'banana' in your proposal to let me know you've read it in detail :-)