Which buck converter, and did you connect it to the 5volt pin?
A load cell amplifier powered by 24volt and then connected to a 5volt input sounds suspicious.
Why did you use that, with the low-resolution Arduino A/D, and maybe with the instability of default 5volt Aref (we didn't see your code). Everybody else uses a 24-bit digital HX711 breakout board.
Leo..