Hello Dejan,
I had a similar problem here:
Unfortunately, I have not been able to reproduce the error too.
In my case, I wrote a small python script, which kept sending requests to my service. In some cases, the error occured after the 10th try - in some cases, it happened after the 70th try. And everytime, I attached a debugger to the process, the problem was gone away.
On other machines, the error never occured. Fortunately on our production environment.
If you find any solution, please let me know. 
I hope, you have more luck than me.
Best regards
Daniel