I changed:
int refresh_rate = 0.0; //Dataloger Refresh Rate
0.0? Do you not understand what an integer value is?
if (currentTime >= lastReadTime + refresh_rate) {
lastReadTime = millis();
File logFile = SD.open("LOG.csv", FILE_WRITE);
logFile.println(sensors.getTempCByIndex(0));
So, lastReadTime is the last time you wrote to the file. I see. Do you have another variable, lastWriteTime, for the last time you read from the file?