I have a reflective “mirror” material as a plane, and some scissors floating in the air and being reflected. I couldn’t figure out why but there were vertical stripes in the reflections which made no sense.
I didn’t have any glare nodes going on in compositing, and was rendering at 1024 samples. Eventually I checked my camera and discovered that putting it at a low angle, halfway in the mirror was causing the stripes. Every day is a learning day with Blender!
ah haha nice! Yeah camera angle is important 
Glad you figured it out and yeah every day is a new adventure in Blender 