Hi Carl,
Why such a difference?
I guess different tests have different standards.
I did a Google lighthouse test for your site, on desktop it looks ok, but on mobile or a slower network environment, the score doesn’t look great.
As you can see you have so many CSS files that are blocking the browser rendering, mostly from plugins and google fonts, the green part is from GP and GP premium, the others are from WP and other plugins.
https://www.screencast.com/t/QoLicOB4y
I would suggest:
1. Remove the font variants which you are not using, for example, your site is downloading regular, italic,700, and 700italic variants of the Archivonarrow font currently.
2. Use a cache plugin to optimize CSS and JS.
Let me know if that helps.