The schematic for the BME280 in the section ESP32 Web Server display sensor readings shows both the CSB and SDO without connections. The Bosch manual specifically states that the CSB must be connected to VDDIO to enable the I2C mode. If pulled low regardless of clock I2C is disabled until next power on reset. For the address of the I2C SDO cannot be left floating! Tied low the I2C address is 0x76, and tied high 0x77. So how can the sensor work?
I do not have the exact model you show in text so the fact that I can’t get mine to work may be my problem since so many of the Chinese vendors pay no regard to BME280 and BMP280. From looking at the listings, if you paid less than $1.50 you got a BMP280 or a non functioning BOSCH ripoff clone.
The above $3.50 may indeed get you a working clone or true BOSCH BME humidity sensor.
The question that remains is with no connections on these pins how does your unit work? My sensor is in fact a BMP280 although purrchased as a BME280 and it does work in the SPI mode with my ESP8266 module. I will attempt to get it operate with the ESP32.
We use this sensor without connecting those pins, and the sensor always works flawlessly without any problems.
(How? I don’t know… maybe it is connected to GND by default internally, because its address is 0x76)
Because we always use I2C communication with the BME280, now we use the version with 4 pins more often. (like the one in this image: https://thumbs3.ebaystatic.com/d/l225/m/m-JQxLVoreFZUc0UbYoLdCg.jpg)
Let me know if you have any problems connecting the sensor to the ESP32.