Slow rendering css

I have noticed for the last few days that when viewing the community forum I have been getting a white page of [forum] text before the css is rendered, about a second later.

I put this down to my IP connection/browser/PC. This weekend I have been away and the same thing happened but on a different PC and connection which would rule out anything to do with my configuration at home.

I do not have this problem with my own hosted phpBB 3.1 site.