https://github.com/adafruit/Adafruit_BME280_Library/issues/21

Author: ladyada

examples/bme280test/bme280test.ino

@@ -50,6 +50,8 @@ void setup() {
     delayTime = 1000;
 
     Serial.println();
+
+    delay(100); // let sensor boot up
 }