Formit sometimes doesn't submit / no feedback

Hey folks, I am experiencing an issue with our contact form, and am having a really hard time determining the source, let alone fixing it.

The form works most of the time, but sometimes on submit the page just reloads - no validation errors are displayed, the user is not forwarded to the "successful submission" page, no confirmation email is sent, and all the form fields they filled out are emptied.

I recently upgraded formit to the latest version, although that did not solve my problem, and my revo version is 2.1.5.

Where would you guys start with this problem?

One of the problems I'm encountering is my inability to reproduce this. I can observe when it's not working and clearing the cache will make it work again, but I'm not sure what precipitates the form breaking.

I have managed to 'copy as curl' the POST though. Here's a pastebin with an example of a successful submission, and an example of a failed submission:

http://pastebin.com/8rjhBDEX

And in case it's relevant:

PHP 5.3
MySQL 5.16
Apache2

Did you check the MODX error logs any info there?

You should also upgrade your MODX install as the latest version takes care of some security vulnerabilities.

Also post your formit and form code to see if there are any issues with it.

I did yep

I checked modx, apache, and php logs, and monitored all when I managed to 'break' the form.

This first page does some form switching - there are several enquiry types:

http://pastebin.com/Ny7uUELt

In addition, the form routes to different email addresses depending on the postal code entered - on the template variables tab for a particular form is a list of postal codes to route emails to. Here's an example of a specific form:

http://pastebin.com/7ttPb6b1