Okay, well when you use one of these boards, it is in effect an Arduino Uno with an ESP8266 as its WiFi modem.
The ESP8266 needs to be running the factory AT commands and the Uno running a Blynk sketch that uses the BlynkSimpleShieldEsp8266.h library.
The problem is, this library doesn’t support RSSI reporting without hacking the Blynk library, as described here…
This makes me think that you are running the sketch on the ESP8266 rather than the Uno.
Can you share your sketch please (correctly formatted with triple backticks of course).
Pete.