PR_CONNECT_RESET_ERROR when sending POST multipart/form-data

I don't see how those SSL/TLS settings could cause such an error.

Does this error occur for every client? Or just a few? On the internet, I saw a few threads mentioning anti virus software like Avast or others causing this error.

It also might be some kind of MTU problem. Not an issue when the packets are small, but causing issues when the TCP packets are fully loaded.