We have a SharePoint 2016 farm. There is a reverse proxy server between SharePoint web server and the Internet users. When user upload a small file (less than 1MB) to a specific path, he always get 413 error. But he can upload the same file to another file without error (using the same browser and same login session).
We would like to investigate what happen to the reverse proxy and Internet gateway but we have no access to it. If we connect SharePoint behind reverse proxy, no error will occur at all.
What could be the cause?