This error is a protocol error.  It is the analog to WSAECONNRESET.
ECONNRESET occurs when the local host receives a RST packet from the peer, usually because the peer closed the connection.
WSAECONNABORT occurs when the local tcp layer decides that the connection is dead, (it may have sent RST to the peer itself).  This can occur for various reasons.  Often because the client has cone away, closed the connection or other things.  It is best to treat WSACONNRESET as WSACONNABORT, i.e., there was a TCP protocol error and the transaction (http request) probably wasn't completed completely by both parties.  See also here:
https://www.chilkatsoft.com/p/p_299.asp

In your case, I would expect a problem with the client uploading the file.  It probably closes the connection after sending the data without waiting for the http response.