Strange post request that only works when fidler is enabled?

Question

C++ / C#

Hello, I have this code

string get = request.Get("https://www.evernote.com/Login.action").ToString();
 
                    string hpts = Pars(get, "hpts\").value = \"", "\"", 0);
                    string hptsh = Pars(get, "hptsh\").value = \"", "\"", 0);
                    string source_page = Pars(get, "_sourcePage\" value=\"", "\"", 0);
                    string fp = Pars(get, "__fp\" value=\"", "\"", 0);
 
                    request.AddHeader("sec-ch-ua", "\"Chromium\";v=\"92\", \" Not A; Brand\";v=\"99\", \"Google Chrome\";v=\"92\"");
                    request.AddHeader("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9");
                    request.AddHeader("X-Requested-With", "XMLHttpRequest");
                    request.AddHeader("sec-ch-ua-mobile", "?0");
                    request.AddHeader("Origin", "https://www.evernote.com");
                    request.AddHeader("Sec-Fetch-Site", "same-origin");
                    request.AddHeader("Sec-Fetch-Mode", "cors");
                    request.AddHeader("Sec-Fetch-Dest", "empty");
                    request.AddHeader("Upgrade-Insecure-Requests", "1");
                    request.AddHeader("Sec-Fetch-User", "?1");
                    request.AddHeader("Accept-Encoding", "gzip, deflate, br");
                    request.Referer = "https://www.evernote.com/Login.action";
                    request.AddHeader(HttpHeader.AcceptLanguage, "ru-RU,ru;q=0.9,en-US;q=0.8,en;q=0.7");
 
                    request.Post("https://www.evernote.com/Login.action", "username=" + login + "&password=" + password + "&login=&login=%D0%92%D0%BE%D0%B9%D1%82%D0%B8&hpts=" + hpts + "&hptsh=" + hptsh + "&analyticsLoginOrigin=login_action&clipperFlow=false&showSwitchService=true&usernameImmutable=false&_sourcePage=" + source_page + "&__fp=" + fp, "application/x-www-form-urlencoded;");

Well, here it is, oddities.
This code worked N amount of time and stopped 2 days ago. In an attempt to determine what has changed in the requests on the site (this is authorization on the evernote site), I realized that there are no changes.
And the strangest thing is that if I turn on the fiddler to track requests, then the code works again ... I almost believed it! help me figure it out plz