Some customers told us their cart will be empty. I tried myself. The cart will be empty in 24 hours. I also tried to log in to add cart, the cart is empty again. The Shopify team told me upgrade the theme. I did but doesn’t work either. Now I am using Dawn the latest version.
Have you tried to login your account using another browser and then add item to cart and check if you get the same issue? If you dont then I guess the issue caused by browser when it refresh browser cache and session automatically.
Yes, I tried with my phone too. It doesn’t work either. I use google chrome. I also upgrade google chrome to latest version. When I contact Shopify team, they tested too, same issue.
The default duration of the cookies in Shopify is 2 weeks.
You can check here https://www.shopify.com/ca/legal/cookies
Once check the apps which are installed in your store and using cookies or overwriting the cart cookies.