ESP32 not giving correct readings unless GND is connected to earth

[since2020]

I am trying to measure the sound level using the code by Ivan Kostoski from GitHub and I observed a strange phenomenon. Unless I connect the GND pin to actual Ground (earth), I am not getting the correct values. I am using ESP32 dev kit v4 and an INMP441 breakout board.

My background is not Electronics so can someone please explain why this is happening and possibilities to overcome this effect. I have been using this equipment from the past few months and everything was fine until now.

Pin connections are as follows:

WS - PIN 15
SCK - PIN 2
SD - PIN 13

Thanks in Advance