In this thread, there's code that can be used to replace the contents of the library file Si7021.cpp viewtopic.php?f=32&t=8002&p=41755&hilit=si7021#p41755
The library itself van be downloaded from https://github.com/LowPowerLab/SI7021
After changing the library file, I get poper output from the basic sample:
BASIC DEMO
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Heater Status = OFF
Humidity : 59.59 % Temp : 20.47 C 30
Humidity : 59.48 % Temp : 20.50 C 29
Humidity : 59.48 % Temp : 20.49 C 28
Humidity : 59.49 % Temp : 20.47 C 27
Humidity : 59.48 % Temp : 20.46 C 26
Humidity : 59.47 % Temp : 20.45 C 25
Humidity : 59.47 % Temp : 20.48 C 24
Humidity : 59.48 % Temp : 20.48 C 23
Humidity : 59.48 % Temp : 20.45 C 22
Humidity : 59.49 % Temp : 20.47 C 21
Humidity : 59.48 % Temp : 20.48 C 20