Font rendering issue needs fixing

Completed site has been live for a while but there is an issue with the @fontface.
We have tried numerous things to fix it but to no avail!
The current issue:
From a cleared cache, the site will load but the font is defaulted in IE and in Firefox for example. Unlike usual where a font will have a slight delay and then load the correct font, this site doesn't until you click on another page. Therefore, it does absolutely nothing until you click on a page.
We've had this on other sites before (that are using the same client hosting) but have managed to fix them), but on this site nothing is working!
We've checked all the usual things -such as where the font commands are on the page and even tried a Fout method to see if that's the issue. However, it is still not rendering correctly, until you physically click on the page.
However, on some browsers that other people appear to be using (IE / Firefox elsewhere) it is allegedly working, so that's even more confusing.
We require someone who is very, very good at this and who can fix it quickly.
Please do not bother applying if you want to guess a solution or indeed if you 'think' you can fix it, unless you're 100% confident that you can we cannot risk an unhappy client.
The answer is probably staring us in the face but we cannot see it!
So if you are good with font face and can see a job through we'll be happy to use you for this job. If you fix it quickly, you will get paid.
For someone who knows what they're doing it should be an easy job. We used a guy for the other two sites and he solved it very quickly, but then he has years of experience so it only took him an hour.
We need someone who can start right now - so no delays and who can get on this today to fix it today.

Once the client has checked the site and can see font loading correctly we will pay straight away with no delays.

Thanks