As I use ESP-12F hardware serial port (D1 & D3) to communicate another controller. After a while on power up, there is the following message on serial port even I disable WIFI (by WIFI.SLEEP):
\nSwitched to AP Mode xxxxxx r\nIP address: 192.168.4.1\r\n
As this message may sometimes block the communication between ESP-12F & the controller.
Thanks!