Coldfusion per application mapping randomly fails

In my application.cfc file I have the following code:

this.mappings["/includes"] = "#expandPath('../../priv/inc/')#";

and then on a page I have the following CF include set up:

<cfinclude template="/includes/imageOptimise-thumbnail.cfm">

For the majority of the time when the page is submitted the imageOptimise-thumbnail page runs without any issue but occasionally it will error saying that it can't find the imageOptimise-thumbnail.cfm. If I resubmit the page, chances are it will work but the question is, why is it sometimes not being able to find the page?

I had a look in the CF Admin and I can't see anything in the logs saying that there was an error but it is clearly showing a Coldfusion 'template not found' error message when it fails.

Anyone got any ideas?