I had two problems. First was that my cart was not updating well. For example, i add one item to it, and click on cart and I see that Item, but when I return on shop page and add one more item and go again to cart, in total I still see only one item, but in cart in menu it shows right amount.
I thought that problem could be cause I used woocommerce 2.6.8. But when I uploaded to it site broke. Now, I can open homepage, and that is it. All other page displays 500 error problem.
This error may be caused by low limits of PHP values. Ask your hosting provider to check this issue, and perhaps increase memory_limit value.
Also I checked your site and different pages, and I didn’t see the error.