@carlfriedrich
I resolved the issue by copying the theme.js from the 1.7.8.0 download (zip file > prestashop\themes\classic\assets\js\) back into the \themes\classic\assets\js\ on my live site. The icons then loaded correctly on all pages - I have attached the file from the latest 1.7.8.0 download if that helps.
Kind regards,
Steven