problem with two SoftwareSerial and Adafruit DataLogger



Do not call begin() on every pass through loop(). Call it ONCE in setup().

  if (Sensor1Serial.available()>0)

You've just started listening. What do you suppose the odds are that data will arrive in the 62.5 nanoseconds between the two instructions?

You don't stand a snowball's chance in hell of listening to two software serial ports at the same time. Either get a Mega or forget this project.