A Configuration mode is a special mode of AC-825 Access control panel that come to reduce data sync time and making sure any update on AC-825 will be effected immediately (as long as the server and AC-825 panel are online). 

When any configuration is made on AxTraxNG (users, time zone, Access Group and more)  that affect the data stored on  AC-825 access control  panel the panel will be set to "Configuration Mode" meaning that any access requested will be notified to AxTraxNG server and AxTraxNG server will send the use Access Data to the panel, this ensure thare revoked uses will not gain access till an update is done on the controller.