Hello. I use a plug-in called user switching (https://wordpress.org/plugins/user-switching/), and more often than not, items that are in the cart when I am admin show up in the cart of the user I switch to, and vice-versa.
Here is an example of the problem:
1. Open two browsers, Chrome & Firefox.
2. Log in as admin in both.
3. Check the carts of both. If there are any products, empty the carts. If not, skip to step 7.
4. Log out of both.
5. Log in as admin in both.
6. Check the carts of both.
– Result: they are empty.
7. In Chrome, add product(s) to cart.
8. In Firefox, navigate to “Users”. Do NOT navigate to cart.
9. In Firefox, switch to a non-admin user.
10. In Firefox, navigate to cart.
– Result: products added in admin account in Chrome are in non-admin user’s cart in Firefox.
This happened when only WooCommerce and Event Tickets Plus were active with the Twenty Seventeen default WordPress theme.