The website has had a prune and new theme added this weekend. There were a few issues with the previous theme conflicting with the Autoptimize plugin, which sometimes locked up the browser on page load, very annoying from a users point of view. I have been meaning to fi it for a number of months already, so apologies if you encountered the error whilst browsing!
This theme was built to avoid using Autoptimize and the like, aiming for speed through minimal use of imagery, avoiding bootstrap, loading a significant portion of the css into the <head> and building functionality into the roots\sage theme rather than relying on 3rd party plugins.
In tests earlier today this site using this theme (NNM 2021) loaded quicker when Autoptimize was deactivated, logging a PageSpeed insights score of 96. Quite pleased with that!