I searched the forum and found this topic which matched my situation:
Topic Link
As I also had an older Mysql Version I asked my host to upgrade it , which they have to 5.6. My WPPizza System Info:
PHP Version: 5.6.32
MySQL Version: 5.6.37-log [mysqli]
Web Server Info: Apache
But in my case the problem is persisting, the order page still says my cart is empty , but if I return to the page I filled the cart on the items are all there.