Verification Token

Hi

I am working on a test with the user action flow : A user opens the
application, Logs in and then logs out

The following are the HTTP requests placed in sequence under a simple
controller under a thread group.

GET Main Page.
GET Login Page
POST Login Page
GET Logout Page.
I also have a cookie manager setup. I am also extracting verification
token from step 2 and passing it into step 3.

All the above setup is working fine for the following scenarios: 1 user,
loop count 1. 1 user, loop count FOREVER.

However, when i run 2 user test with FOREVER option, the samples are
fine most of the time but after a period of time i am noticing the POST
login page step as failing due to request verification token not
matching the cookie. It sometimes shows request verification token is
not matching and it is inconsistent.

The failure seems to be appearing only on 10% of samples for Post login
page and not for all the samples.

Could someone help me . if is there any reason why my server is throwing
a verification token mismatch only few times(10% of the time) but not
always?

Thanks