Q:

Web server resets post request randomly when going over ssl

I've got a web server with Apache 2.4.12 running on a virtual Ubuntu 15.10 machine.  Often, but completely random, I get a connection reset (flag is RESET in iptraf) when submitting a form (post-request to the server). 
The strange thing is that it's completely random, I could not find a way to reproduce this consistently.  It can happen 5 requests with the connection reset and then suddenly it will start working again.  When waiting a bit, the first request mostly fails (reset).  The server is not behind a firewall and is connected directly to the modem. 
I've already tried to check the logs, but Apache does not receive the request at all.  When doing post requests while having iptraf open, it shows 'RESET' on the flags-column when the request fails.  The browser will then throw an error that the web server has dropped the connection unexpectedly. 
After further testing, it seems to be related to CodeIgniter 3.1 (PHP-framework) the Apache vhost, which is using SSL.  I have no clue what is causing this random connection-resets only on a post-request, as the CI-configuration-file seems fine to me.  I've tried submitting forms (non-CI) from a different virtual machine on the same host (using the same NIC) and it was working fine without dropouts. 
After the discovery that it works well on another server, I've run the same script on the server that is hosting the CodeIgniter-project (note that this is non-ssl), and it's working every submit.  Then trying again within the CI-environment (this is ssl), and it fails again most of the times. 
I will now try to discover what is causing this, as I have a complete identical copy of this project running on a completely different server in a different location, which is working fine without this problem.  Could this be something server-software-related that is causing this 'bug?'  in CI Apache ssl? 

A:

This 'bug' has been fixed by reinstalled this particular vm.  I think something must have been corrupted as I had updated Ubuntu 14.04 LTS to 15.10 and it gave me a lot of errors in the process. 
I managed to get the vm working again, but apparently, ssl on Apache was broken.  Still no clue what exactly caused this, but it seems to be fixed not on a fresh 15.10 Ubuntu x64 installation.