HTTP server response 409 // Google web app - google-apps-script

Question

I'm having issues lately with my web app written in Google Apps Script.. From time to time it doesn't load properly and returns a 409 response.. It seems as it has no real reason, it's randomly. If I try to reload the page sometimes it loads properly, sometimes returns 409. The issue also just occurs some days and times. I can't figure out what can be the reason, the only thing I've noticed is that when the issue occurs also Google Apps Script Program seem to be slow / failing (for example takes longer than usual to save a file, sometimes fails on saving or showing logs etc).
Screenshot from web inspector when the issue occurs..
If the issue is on Google's end on their servers I guess there's not much I can do, but still checking if anyone else experienced these issues? Or is there anything I can do?
Also want to make sure it's not in my code.. I'm not in anyway a pro when it comes to programming, but a happy amateur. But if it was in my code, at least in my mind it would fail every time and not just only sometimes? I googles a bit and found on this site that when making POST requests you need to have your parameters correct, I'm using Twilio in my script but it's in a separate function and is not initiated when the script loads and I have it written as the linked documentation suggests..
Inserting some code snippets here - if anyone sees something that looks weird or could be the reason for my issues I would much appreciate your help!
SMS Function - can this be the reason??
function sendSms_(to, body) {
var messages_url = "https://api.twilio.com/2010-04-01/Accounts/ACe5***************/Messages.json";
var payload = {
"To": to,
"Body" : body,
"From" : "Killnoise"
};
var options = {
"method" : "post",
"contentType": "application/x-www-form-urlencoded", //This line I added after reading the linked documentation
"payload" : payload
};
options.headers = {
"Authorization" : "Basic " + Utilities.base64Encode("AC********************:f8be***************")
};
try { UrlFetchApp.fetch(messages_url, options); } catch(Err) {}
return;
}
doGet function - anything wrong here??
function doGet(e){
var staffId = e.parameter.staffId;
var key = e.parameter.key;
var lang = e.parameter.lang
// staffId = "S102", key = "abc"
if(auth_(staffId, key, lang) == true){
var output = HtmlService.createTemplateFromFile('StaffHtml').getRawContent();
/*/
Am I doing right above and below when the output is returned? I'm a bit green
here - should I write this in another way? Not seeing this could be the reason
for my current issue though..
/*/
output = output.replace('{{selectAlert}}', language('selectAlert', lang));
output = output.replace('{{takenAlert}}', language('takenAlert', lang));
output = output.replace('{{declineGivenAlert}}', language('declineGivenAlert', lang));
output = output.replace('{{beta}}', language('beta', lang));
output = output.replace(/{{surgePrompt}}/g, language('surgePrompt', lang));
output = output.replace('<%staffId%>', lang + staffId);
output = output.replace('{{invitationSent}}', language('invitationSent', lang));
output = output.replace('{{timeOutAlert}}', language('timeOutAlert', lang));
output = output.replace('{{newNotifications}}', language('newNotifications', lang));
var out = HtmlService.createHtmlOutput(output)
.addMetaTag('viewport', 'width=device-width, initial-scale = 1, user-scalable = no')
.setTitle('Killnoise').setXFrameOptionsMode(HtmlService.XFrameOptionsMode.DEFAULT);
return out;
} else {
return HtmlService.createHtmlOutput('Invalid URLS');
}
}