[Barrow4491]

Once the HTU21 can't be directly attached to the PCB (pinout on the PCB is for the SHT31) make sure the cables between the PCB and sensor are the shortest as possible.
The OLED display should be connected directly on the PCB.

I have just tested an unit with the HTU21 and latest software, and it is working fine. Double check if the installed HTU21 library is the one supplied with the software package.

Werk,
Back home after an extended absence, trying to solve the freezing problem but now have an issue with compiling, and have attached the relevant portion of the error message.
I am using IDE 1.8.9 and ESP 8266 board manager 2.4.2
I note that you recommend the SHT31 T/H sensor in lieu of HTU21D and am waiting for mine to arrive.
Regards
Jim
 

Code:

 
       In file included from C:\Users\JBA\Documents\Arduino\WeatherDuino_AQM_II\v120\software\WeatherDuino_AQM_ESP8266_ASK_v120_b006\WeatherDuino_AQM_ESP8266_ASK_v120_b006.ino:3:0:

C:\Users\JBA\Documents\Arduino\libraries\HTU21D/HTU21D.h:31:7: error: previous definition of 'class HTU21D'

 class HTU21D {

       ^

Using library ArduinoOTA at version 1.0 in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\ArduinoOTA 
Using library ESP8266WiFi at version 1.0 in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\ESP8266WiFi 
Using library HTU21D in folder: C:\Users\JBA\Documents\Arduino\libraries\HTU21D (legacy)
Using library Wire at version 1.0 in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\Wire 
Using library ArduinoJson at version 5.13.2 in folder: C:\Users\JBA\Documents\Arduino\libraries\ArduinoJson 
Using library SoftwareSerial at version 1.0 in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\SoftwareSerial 
Using library Timer in folder: C:\Users\JBA\Documents\Arduino\libraries\Timer (legacy)
Using library ESP8266HTTPClient at version 1.1 in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\ESP8266HTTPClient 
Using library ESP8266WebServer at version 1.0 in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\ESP8266WebServer 
Using library ESP8266mDNS in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\ESP8266mDNS (legacy)
Using library TimezoneESP8266 in folder: C:\Users\JBA\Documents\Arduino\libraries\TimezoneESP8266 (legacy)
Using library Time at version 1.5 in folder: C:\Users\JBA\Documents\Arduino\libraries\Time 
Using library RadioHead in folder: C:\Users\JBA\Documents\Arduino\libraries\RadioHead (legacy)
Using library SPI at version 1.0 in folder: C:\Users\JBA\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.4.2\libraries\SPI 
Using library esp8266-OLED-SSD1306 at version 3.2.7 in folder: C:\Users\JBA\Documents\Arduino\libraries\esp8266-OLED-SSD1306 
Using library Adafruit_SHT31 at version 1.0.0 in folder: C:\Users\JBA\Documents\Arduino\libraries\Adafruit_SHT31 
exit status 1
Error compiling for board LOLIN(WEMOS) D1 R2 & mini.