Response Sent To Wrong User

[Yaoxing]

Hi all,
I'm suffering from the pain that Nginx returns wrong page to the users.
Don't know if anyone else encountered the same problem.
I have a page summaries.aspx which displays the user summary info for
users. No query string is required, the page just get current user ID
from session, and load the info of this user. Most of the time,
everything works fine. However, if the website is under heavy stress,
Nginx probably would return this page to a wrong user. For example, I'm
a at a.com. If the site is under heavy stress, Iwill see another user's
summary page.
I'm pretty sure this does not happen in .net side because without nginx
this will not happen.
Could anybody give me some suggestions?
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Regards,
Yaoxing