I'm using LockService when sending emails, but when multiple users run it at the same time, it throws the error: Service invoked too many times...

Here's some log, showing the failures:

function sendEmail() {
  const ss = SpreadsheetApp.getActiveSpreadsheet();
  var lock = LockService.getScriptLock();
  try {
    lock.waitLock(3000); // wait 03 seconds for others' use of the code section and lock to stop and then proceed
  } catch (e) {
    Logger.log('Someone has just sent an Email. Try it again 3 seconds later.');
    return HtmlService.createHtmlOutput("<b> Server Busy please try after some time <p>")
    // In case this a server side code called asynchronously you return a error code and display the appropriate message on the client side
    //return "Error: Server busy try again later... Sorry :("
  }
  
   /*
   Gets certain data from current row. These are used as criteria
   */

    GmailApp.sendEmail(email, "Text", name + " BODY.", { name: 'Diplay Custom Name as Sender' });
    
//Looks for a matching record in another sheet to mark its adjacent column as sent ("Yes")
    for (var n = 0; n < formRespValues.length; n++) {
      if (formRespValues[n][1] == testNo) {
        formRespSheet.getRange('M' + (2 + n)).setValue('Yes');
      }
    }
  }
  SpreadsheetApp.flush(); // applies all pending spreadsheet changes
  lock.releaseLock();
}