Possible solutions:
1. Check the LAN connectivity of the controller and server by pinging controllers from the Access360 server
2. Controller ports should not be blocked on server and network
3. Login to Application Manager, Go to View>Assign Branch. None of the branches should be checked. Go to Services>Application Services should be running
4. In Application Manager, the Application service error log should be checked for any real time error causing the disconnection
Check the port mentioned in the application manager and controller webpage is the same.