Have been struggling with this problem for some time now and its a bit confusing. The problem is the following that my cart drops the products added when I visit a new category on the site.
When FPC is disable all works fine.
Have been testing and testing and have found out the the problems occur when the page on the site is not cached. If I have visited the site one time before then its not problem to add the product, but is the category/page in the cache all the items in the cart is droped and when I add the product from the unpages cached this will be the number 1 item in the cart and the other is gone.
Need to find a solution for this problem so I can put the site live and replace my M1 current site. Or maybe M2 is still to full of bugs so its better to wait some time.
There is not problem at all when the FPC is disable then all the items remain in the cart.
Magento 2.3. site: http://kasperstestdev.prod42.magentohotel.dk/
Happy new year btw :)