HTTPS POSTS sometimes not getting to apache
This article walks through a series of approaches for debugging Apache httpd, Debugging Apache Web Server Problems:


  Debugging requests and responses
  
  When supporting web applications, there are times when a problem can
  be caused by an application server, proxy server or the web server
  itself. To troubleshoot these types of issues, it is useful to dump
  the HTTP requests and responses to isolate the problem to the local
  system, or a remote system. The apache web server module mod_dumpio
  can be used for this purpose, since it allows HTTP requests and/or
  HTTP responses to be written to the error_log.


Alternatively, is your httpd instance occasionally saturated with requests and dropping new connections?

The techniques in the link above should help you isolate which part is encountering problems.

Failing that, try the Webmasters StackExchange; you may find more experienced people there.