Incorrect Shipping Zone displayed after enabling Caching CDN!

Hello,

after enabling caching and cdn service to speed up website delivery, I have discovered that the shipping zone used by the free shipping bad variable seems to default to the United States (£85GBP).

I have a total of 5 shipping zones. Only 3 and 4 below have the same shipping cost value for the zone (£85GBP).
1. UK
2. EU
3. North/South America
4. Asia
5. Oceania

Is there a way to fix this so the plugin and my configuration can co-exist?

Regards
George