I has same problem. I solved it by adding sht30.init(); to the setup() function.

SHT3X sht30;
QMP6988 qmp6988;
float tmp = 0.0;
float hum = 0.0;
float pressure = 0.0;

void setup() {
M5.begin();
Wire.begin();
sht30.init();
qmp6988.init();
}

this is missing in the example