PDF generator drops every 5th time

Hi,

I have the plugin installed a month ago, changed into live modus about a week ago. I am handling about 200 pdf creations and sendings per day in the moment. It seems that when two people filling out the form almost same time one of them is getting following error

There was an error generating the PDF file.
Your server wasn't able to upload PDF file: read function returned funny value

I was able to trace this through the last days and have made following discoveries:
The time between pushing the “Send” button in the form and the automatic forwarding is about 10 seconds with my installation and having somebody else pushing the “Send” button a different computer just in this time frame seems to produce an abort on the first one.

I now disabled the attaching of the PDF and just send the download link to reduce failures. I was able to reproduce the same problem with just clicking on two pdf links almost the same time.

Am I right that the plugin is not able to queue PDF creating jobs?