User unable to login

Hello - A few of us have gotten the below message since the conversion to TS Go. I myself just closed and reopened my browser and was able to get in. Our CFO restarted her computer and was able to get in. We now have a user who, despite both a restart and a shut down, is still unable to get in and is still getting the below error message. Nothing has changed for any of our users since the set up. Any ideas why this happens and how to fix?