I contacted Woo.com yesterday thinking it was a WooCommerce issue, but I think it has to do with the plugin. Below is the contact with Woo.com (our website: kamadoexpress.nl):
If someone adds a BBQ of a certain amount into the cart, they get a free “starter pack” (“startpakket”). 6 free products then get added into the cart. But they don’t show up the first time the cart page loads…. They only show up after a reload of the cart page.
You should see that the cart in the shop menu / header already says 7 products in cart, but if you go to the cart it only shows the BBQ. Then if you reload the page it shows the other products correctly.
If I go from the cart page to another page and then back to the cart, the products also won’t show up.. If I then reload the cart page the products will show up..
I see. I recommend that you reach out to the plugin developers for further testing. It does seem that there is a bit of delay before the “function” kicks in so you have to reload for the browser to recognize the cookie.