Can't add data to existing SD file

  • Hi,
    I have ported my datalogging program from Arduino Mega to the M5Stack Core 2 for AWS.
    It all is now working as I expected except for one behavior.
    On the Arduino, I could open an existing file on SD card and append data to the end of the file.
    On the M5Stack, I can create, open, write to, and close a file on the SD card.
    But when I re-open this file and write more data, it overwrites the existing data in the file.
    It appears the FILE_WRITE specifier is allowing write access but is not moving the file pointer to its end...not sure why not?
    Can anyone suggest what I am doing wrong or provide a workaround?

    The relevant portion of my test code is below; apologies if it comes through with weird formatting:

    if (!SD.begin(4,SPI,40000000)) { // ******M5 CS line is GPIO4
    Serial.println("initialization failed!");
    while (1);
    Serial.println("initialization done.");

    // open the file. note that only one file can be open at a time,
    // so you have to close this one before opening another.

    NewFile ="/TRIAL.TXT",FILE_WRITE);  
    char message1[64]="This is just a test";  // 64 byte array
    char message2[64]="It seems to be working so far!";

    // delay(5000);
    // if the file opened okay, write to it:
    if (NewFile) {

    // close the file:

    } else {
    // if the file didn't open, print an error:
    Serial.println("error initially opening test.txt");

    // Now try reopening file and writing more data into it

     NewFile ="/TRIAL.TXT",FILE_WRITE);  //*******Reopen for more writing
     NewFile.println("Trying to add this additional line");