Understanding WiFi.printDiag(Serial)
Mode: AP


In access point mode. Can also be STA or STA+AP for Station or dual role modes.


  PHY mode:N


Physical interface mode. At the moment it's in 802.11n mode. Depends on the AP you are connecting to if any.


  Channel: 1 


Which WiFi channel you are communicating on

All the following are meaningless in AP mode. They only pertain to STA mode:


  AP id: 0


Internal ID of the access point you are connecting to, if any.


  Status: 255


Connection status


  Auto connect: 1 


Automatically connect to an access point.


  SSID (0):       


Name of the access point currently connected to.


  Passphrase (0):  


Password used to connect to the current access point


  BSSID set: 0


BSSID (kind of like the MAC address) of the access point connected to.

As you can see, much of it is meaningless for access point mode, since it mostly is to do with connecting the ESP8266 to an existing network.  In AP mode there's not a lot of debugging information you can get - "is it running?" is really all there is.