LineItem ID can be duplicated in serializable cart in load-balanced environment

Description

In a load-balanced environment, the load balancer distributes client requests or network load efficiently across multiple servers. So it's possible that requests of the same client are processed by different servers. If those requests were for adding line items to a cart, the line item id might be duplicated in the same cart.

See more detail on the thread (last comments):
http://world.episerver.com/forum/developer-forum/Episerver-Commerce/Thread-Container/2017/5/litemitemid-resetting-on-iis-reset/?pageIndex=1