EDIT
Apologies, this seems to have fixed itself now?
I cleared down my site cache & cloudflare CDN cache and seems to be OK.
Please feel free to close this post or delete it.
The category and manufacturer page title used to use the "oswald" font, but I just noticed that within the last few days, this has not been used anymore.
I checked templates/my-template/html/com_virtuemart/assets/css/flexibleVM2Global.css and I see that the font is called here;
@import url(https://fonts.googleapis.com/css?family=Oswald:400,300);
But when I check the front of my website, the "oswald" font seems to be greyed out and reverts to the next font Arial.