Weird Safari (OSX/iOS) script_enqueuing bug

Looking for some advice. One page of my blog is an angular app that is loaded via systemjs. It loads fine in Chrome on my computers and Android phone.

But Safari is a nightmare on OSX and iOS (but worse for the latter). It generally does not load - none of the angular stuff launches - but can do very occasionally. After a massive hunt I found that commenting out the sage_js script enqueuing in /lib/assets.php enabled faultless loading on iOS. Even commenting out all of main.js is insufficient.

Needless to say I need this script loaded too to complete the functionality on e.g. the navbar. I’ve tried playing around with the script loading order but that hasn’t helped. I’d welcome any suggestions.