Giuseppe Tuttobene

Hello guys. I've a pretty several problems with a job. The particles are flickering and I don't understand why. I used a popnet to create a flux of particles and I instanced spheres on the points but when I render the color of the points changed frame by frame and it's evident. What do you think it could be? I tried to color the sphere (piece) differently with color node, attribute from map etc but the problem is the same. Maybe is caused by the 2 timeshift nodes that offset the flux of particles to create a flawless looping video.
here is a video of the flickering: