@Baomei Fan (PACTERA TECHNOLOGIES INC) Thanks for reaching offline.
As discussed, we have tried to clear the cache, password and history of the browser and see if it helps you to sign in with another account, but it didn't help.
Then we used different connectors, and we were able to authenticate with different accounts. We further troubleshoot and logout from the devops site as it was getting the cached credential directly.
When we try to authenticate the connector again then we were able to see the pop up to login with different account and it resolved the issue.
In case someone else facing the similar issue then please make sure that you logout from the devops and then try to authenticate with different account at the connector end.