pre flight HTTP OPTIONS call timesout with 500 Error sporadically - azure

I have a C# based webAPI hosted on Azure WebApp.
Sporadically, the HTTP OPTIONS call fails with a 500 error.
The OPTIONS call is not handled by our code. So I assume the server handles it by itself.
I tried enabling logs but both event log and web server logs does not print anything other than that it failed with a 500 error.
Any ideas why this would happen?.
Update:
I see only the below error messages in the web server logs. No details
Additionally I added code in my webAPI to handle options call, but the code does not go there. Not sure if I need to enable/disable something in web.confi.
2017-08-31 11:49:39 xxx.mywebsite.com OPTIONS /api/apiname StartDate=2017-08-25&EndDate=2017-08-31&X-ARR-LOG-ID=d86ffe7f-32c9-410b-8116-65833d5af7b9 443 - xxx.xxx.xxx.xxx Mozilla/5.0+(Windows+NT+6.1;+Win64;+x64)+AppleWebKit/537.36+(KHTML,+like+Gecko)+Chrome/60.0.3112.113+Safari/537.36 - www.website.com 500 121 0 636 1612 230013

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Http error 400 with HttpSubStatus 607 without a reason

in azure web sites logs,
we see from time to time,
http error code 400 (HttpStatus) with HttpSubStatus 607.
the description is empty for this HttpSubStatus.
can you help describe the reason for IIS logging HttpSubStatus 607?
what can fix this, as this is an IIS error, and not webapp ?
the internet is silent about HttpSubStatus 607.

Flask, FastCGI and 500 HTTP status because of warning

Python flask app with 4 endpoints, 3 of them works fine.
Main one, that handles GraphQL query crushes with 500 Internal server error.
The application works on IIS 8.5 with wfastcgi.py module.
IIS error handler shows this stack:
Warning — MODULE_SET_RESPONSE_ERROR_STATUS
ModuleName — FastCgiModule
Notification — EXECUTE_REQUEST_HANDLER
HttpStatus — 500
HttpReason — INTERNAL SERVER ERROR
HttpSubStatus — 0
ErrorCode — The operation completed successfully. (0x0)
ConfigExceptionInfo
I launched source on flask dev server, and GraphQL handler is working as it used to be.
Founded some solutions about disabling in IIS config Custom Error — not working for me.
By the way, requests on this endpoint, that must cause client errors ( bad request, UNAUTHORIZED, forbidden ) resolves as they used to be.

Getting HTTP error 400- Header too long error

I am getting HTTP 400- Header too long error, I have tried most of solution over internet, but none of them seemed to be working (solutions are like adding reg entries, etc).
I have a sample web application which is calling a web api on my system, but I am getting below error in HTTPERR log file:
2019-11-16 16:58:59 ::1%0 1213 ::1%0 80 HTTP/1.1 GET
/WebApplication2/api/values - 400 - RequestLength -
Here is my code which is calling the web API:
HttpWebRequest GETRequest = (HttpWebRequest)WebRequest.Create(URL);
GETRequest.Method = "GET";
GETRequest.ContentType = "application/json";
GETRequest.Headers.Add("Authorization", "<Something Big value>");
WebResponse GETResponse = await GETRequest.GetResponseAsync();
It is recommended to capture ETL log via
https://blogs.msdn.microsoft.com/wndp/2007/01/18/event-tracing-in-http-sys-part-1-capturing-a-trace/
Then you could use network monitor to analyze both request payload and etl log.
It will help you find the root cause.
Besides, can you find the 400 error in IIS log? Now that the 400 error appear in httperr log. It looks like http.sys blocked the request before it reach IIS server.
If you can find the 400 error in IIS , then you could try to modify the limitation in system.web/httpRuntime and request filter.
If the 400 error only can be found in httperr log. Then you may have to try to make some change in http.sys registry.
https://support.microsoft.com/en-us/help/820129/http-sys-registry-settings-for-windows
Please remember to reboot server to activate these registry!

Error 500 not leaving a "xml" in "Failed Request Tracing Logs" (Azure)?

I have an app in Azure and I'm monitoring that every request is HTTP 200 (OK)
Yesterday I had many errors HTTP 500 and I went to "Diagnose and solve problems > Failed Request Tracing Logs" and for each of these errors there was a .xml with the detailed information.
Thanks to these logs I solved the problem in my app and deployed again. After this all the requests were HTTP 200.
But today something happend and I had 17 errors HTTP 500:
And then I went to "Diagnose and solve problems > Failed Request Tracing Logs" but there are no .xml for these errors.
I thought: maybe Azure is not logging anymore, so I provoked a 404 but the .xml appeared there, so...
Question: Why I don't have 17 xml for these HTTP500 ?
If I turn on "Failed Request Tracing", I can get the failed requests logs, please make sure you have enabled it.
Failed Request Tracing
Failed requests logs
Besides, the failed requests logs should be stored in /LogFiles/W3SVC#########/ folder, you can go to that folder using Kudu Console and check if the logs are there.

HTTP 503 error accessing Sharepoint excelservice.asmx through SOAP

I work for The Smeal College of Business at Penn State. I am doing a project for the Supply chain program and I am creating an excel workbook in Sharepoint that uses a lot of UDF's. I have no problem accessing the workbook or using other UDF's, but when I try to use OpenWorkbookForEditing() I get the following stack trace:
System.Net.WebException: The request failed with HTTP status 503: Service Unavailable.
at System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse(SoapClientMessage message, WebResponse response, Stream responseStream, Boolean asyncCall)
at System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String methodName, Object[] parameters)
at ClassName.ExcelWebService.ExcelService.OpenWorkbookForEditing(String workbookPath, String uiCultureName, String dataCultureName, Status[]& status)
at ClassName.ClassNameFunctions.testWriteCell()
Additionally, I've tried to access excelservice.asmx through PHP SOAP and have not received a response. Each attempt to connect to this service provides a 503 error in the IIS logs similar to the following:
2012-08-06 15:14:58 xxxx::xxx:xxxx:xxxx:xxxxxxx POST /_vti_bin/excelservice.asmx - 80 - xxxx::xxx:xxxx:xxxx:xxxxxxx Mozilla/4.0+(compatible;+MSIE+6.0;+MS+Web+Services+Client+Protocol+2.0.50727.5456) 503 0 0 59
I've tried changing most of the settings in Sharepoint Central Administration, as well as some of the setting in IIS. Does anyone know what could be causing this problem? Thanks.
I'm running a Sharepoint 2010 server on Windows Server 2008.
Can take a look at this article maybe it will help.
http://technet.microsoft.com/en-us/library/ee513104.aspx
The solution that is suggested here is to just restart. If this is a dev machine that shouldn't be a big deal.
Also make sure that no application pools have stopped as this could make the service unavailable.

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