ESP8266-01 wrong flow control settings
AT+UART_DEF=9600,8,1,0,3


Are you aware that this configuration (3) as a rule would require both RTS and CTS extra physical signals to work ? That means, if you do not connect anything there, the level present at some pin configured anywhere would prevent ESP8266 from receiving further data from serial.

In general people use "no flow control" (0)

AT+UART_DEF=9600,8,1,0,0