I am trying to perform load testing on NodeJS application, the application allows single login session for an user. 

But, when i tried to perform load testing with 8 concurrent users (using the same credentials) it was working. 

So, i tried to create 10 user IDs and added to the CSV file and configured "CSV Data Set Config" and "HTTP Cookie Manager" and set the "Number of Threads" to 80.

When I run the test plan, the credentials are not passed to each sessions equally. for example, userID1 is passed 3 times and userID2 is passed 7 times.

Can you clarify the reason for this behaviour and how to run the threads with each credentials (8 sessions for every credentials) from csv file ?