What are the possibilities of showing 4G signal after black screen of iPhone in wireless environment

 What are the possibilities of showing 4G signal after black screen of iPhone in wireless environment

 The following may cause the iPhone to display 4G after locking the screen in a wireless environment：

1)      Disable broadcast probe response is turned on

2)      No authentication of Portal environment, ios and external network probe messages do not work

3)      terminal can not get DNS, the terminal can not resolve and also think that the wifi does not work

4)      Portal or export link quality is poor, ios will remember the SSID behavior

5)      weak signal, ios terminal drop active cut 4G

6)      power saving mode, ios terminal active disconnect