Shopping cart empty bug – how do I fix it?

http://www.thegadgethut.co.uk
Its an amazon affiliate website.

on and off there is a bug where after clicking ad to chart then checkout it returns the page /checkout and says your shopping cart is empty.

Ive tried many things. Ive removed all the plugins but still not luck. Ive re-installed them and turned them off for the min but still no luck.

However if you then click around on the site e.g. “home” it re-populates the cart (in the bar at the top) and you can then click it and checkout…