Tango1

I was wondering if anyone can help me with a problem on my N Lowii. It has got black spots on some of the leaves / shoots which seems to stunt the growth where they are. The rest of the shoots are healthy with good traps and growing well. I have been growing this for a couple of years without any problems until these appeared. Does anyone know if this is some sort of disease, a pest or just a problem with my cultivation ?