uWSGI raises OSError: write error during large request

It may be the case that when you upload things, you use chunked encoding.
There is uWSGI option
--chunked-input-timeout,
that by default is 4 seconds (it defaults
to value of --socket-timeout, which is 4 seconds).

Though problem theoretically may lie somewhere else, I suggest you to try
aforementioned options. Plus, annoying exceptions are the reason why I have

ignore-sigpipe=true
ignore-write-errors=true
disable-write-exception=true

in my uWSGI config (note that I provide 3 options, not 2):

• ignore-sigpipe makes uWSGI not show SIGPIPE errors;
• ignore-write-errors makes it not show errors with
  e.g. uwsgi_response_writev_headers_and_body_do;
• disable-write-exception prevents
  OSError generation on writes.