Hi all,
Something just wasn’t sitting right in my mind, went back and check all the paths, they were all correct, triple checked everything else and still no cigar.
Remembered I had recently added a sub domain for serving images and the like… seems that WordPress categorises fonts with images and videos.
Dug a little deeper and discovered it was a CORS policy issue.
Added code to the sub domains config file for Nginx as recommended on https://serverfault.com/questions/162429/how-do-i-add-access-control-allow-origin-in-nginx and it is now all back and working again!