We have some users reported they cannot upload files to a document library. They are using Chrome and drag/drop some files. Total file size is less than 1MB.
After drag the files to the document library, an error shows up like:
Sorry, your files couldn't be uploaded. The upload might be too large or the server might be experiencing high network traffic.
We are using SP2016 on-premise. The ULS logs are:
Exception occured in scope Microsoft.SharePoint.SPFile._SerializeToJson. Exception=System.IO.FileNotFoundException: The system cannot find the file specified. (Exception from HRESULT: 0x80070002)
SocialRESTExceptionProcessingHandler.DoServerExceptionProcessing - SharePoint Server Exception [System.IO.FileNotFoundException: The system cannot find the file specified. (Exception from HRESULT: 0x80070002) Unknown SPRequest error occurred. More information: 0x80070002
After further test, we found the error is most likely occur when it is the first file user upload. If the same user upload another time for the same file, it success (some users need to try 3rd or 4th time).
Also, error only occur if user upload file by "Drag & Drop".
User tried to troubleshoot with F12 tool and get Status Code: 413 Request Entity Too Large. I found 413 is a FAQ but all solution I found is for custom JSON or WCF solution. Our problem is occurring on OOTB library. The only different is we have setup reverse proxy server between WFE server and the Internet users. The delay (maybe around 1sec) may trigger the error randomly. Also when they upload file in this way, the upload progress bar will keep shaking left and right (not always progressing, sometimes it is descending).
How can I further troubleshoot it and solve it?