The problem:

During the last cleaning, the cleaning nozzle got stuck inside the pipe.
Now, the Sighted Nozzle is sent in to pinpoint the cause. 

Inspection tool used: 
wireless camera, part N° 00700001

Despite cleaning the pipe just a few days ago, there are still deposit remainders in the pipe.

The first damages become visible.

Now it is obvious why the nozzle got stuck here.