Load the another customer's information

Hi,
I have used Nop 3.9. I am involved in a strange issue which I have seen sometimes.  

Some new customers registered successfully, and when they go to checkout page, they see the shipping address of another customer! The information is usually the earlier customers who registered or place an order. When they refresh the page, they see the correct information.

Do you have any idea? How can I fix it and what is the issue?

Thanks

You may want to try adding a machine key to the web.config file.
(see FAQ)

Thank you New York,
I will do your solution.
This issue started when I change the server and I copy all files and DB from the old server to new one.
Users are not logged out, but they can see another customer's billing addresses.