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Is there any way to prevent that the customers in our eStore check out anonymously??
I looked at all the caching and made sure nothing was being cached. However this did not fix the issue.
I did some more research and found that in your code of the plugin you are not calling session_start(); when adding or removing an item from the cart. If added the function on line 74 and 162 in eStore_ajax.php.
Now the cart seems to work just fine.