Odd that some pages load and others don’t; presumably trying to load different elements on different pages and tripping over something.
As extra info – on the off chance it helps in the longer term – switching user agents using the developer tools sees the same pages fail in Safari, Chrome, and Edge, but load in Firefox. 
EDIT
For anyone with this issue, you can get pages to load by:
- Safari
- Settings
- Advanced
- Show features for web developers (enable)
- Safari
- Develop
- Feature Flags
- Worker asynchronous URL error handling (disable)
- Reload the page
