Google Script onChange trigger executes when no change made (overnight)

I have a Google Script running the sendEmails() function with the installable onChange trigger. This works well but I'm seeing that it also executes overnight, when no changes are made to the spreadsheet.

Anyone know what may be happening/ how to prevent this?

Here's the code that's running in the script editor:

/**
 * Sends emails with data from the current spreadsheet.
 */

function sendEmails() {
var sheet = SpreadsheetApp.getActiveSheet();
  var startRow = 2; // First row of data to process
  var numRows = 1; // Number of rows to process
  // Fetch the range of cells A2:C2
  var dataRange = sheet.getRange(startRow, 1, numRows, 5);
  // Fetch values for each row in the Range.
  var data = dataRange.getValues();
  for (i in data) {
    var row = data[i];
    var emailAddress = row[4]; // Fifth column
    var message = row[0]; // First column
    var subject = row[3]; // Fourth Column
    MailApp.sendEmail(emailAddress, subject, message);
  }
}

In the executions/trigger log I see that a trigger executed last night at 5:07 am and the night before at 1:16am, when no changes were made to the spreadsheet

screenshot of trigger log

Wasn't able to figure out the underlying issue, but created code which prevents the script from sending an email (to Asana to create a task in this case) for any row where an email was previously sent.

var TASK_SENT= "TASK_SENT";

/**
 * Sends non-duplicate emails with data from the current spreadsheet.
 */

function sendEmails2() {
  var sheet = SpreadsheetApp.getActiveSheet();
  var startRow = 2; // First row of data to process
  var numRows = sheet.getLastRow();
  // Fetch the range of cells UPDATE
  var dataRange = sheet.getRange(startRow, 1, numRows, 48);
  // Fetch values for each row in the Range.
  var data = dataRange.getValues();
  for (var i = 0; i < data.length; ++i) {
    var row = data[i];
    var message = row[45] //Next Steps Column
    var staff = row[1] // Your Name Column
    var internal_part = row[7] //Who was the Check-in with? Column
    var external_part = row[13] //What Site was your Check-in With? Column
    var check_dt = row[2] //Date of Contact Column
    var check_dt = Utilities.formatDate(new Date(), "GMT+1", "MM/dd/yy")
    var site_disc = row[8] //What site was discussed?
    var emailAddress = row[46]; // Email address column
    var taskSent = row[47]; // Task_Sent column
    if (taskSent != TASK_SENT) { // Prevents sending duplicates
      var subject = staff + " " + 'check-in w/' + " " + internal_part + external_part + " " + 're:' + " " + site_disc + " " + check_dt + " " + 'Next Steps';
      if (emailAddress == "") {
        continue;}
      MailApp.sendEmail(emailAddress, subject, message);
      sheet.getRange(startRow + i, 48).setValue(TASK_SENT);
      // Make sure the cell is updated right away in case the script is interrupted
      SpreadsheetApp.flush();
    }
  }
}