This will happen if your connection is interrupted for any reason. Your connection should automatically resume if you did not use CAC as your verification method when signing in and your organization has the Session Resume policy enabled.
We value connection integrity, so any little interruption in network connection to our Silo servers will prompt a reconnection. If you change internet connection or connect/disconnect to a VPN, you will see this error window. If you believe this is happening without a network connection change occurring, please contact Support
Please contact Support if you have any additional questions and/or require further information.