**Update**
I had a backup of the previous versions of the theme and the Swift Framework plugin so I rolled them both back and my website appears to be working as it was before the update.
This isn’t ideal but is a quick fix so paying customers can continue access to premium content. (I’ve already been fielding phone calls all morning from grumpy subscribers.)
I’m still very much interested in a fix for this issue and if you can help I’ll roll my theme/plugin to the latest during non-peak hours and put the site in maintenance mode to troubleshoot.
Thanks.