Cycles hair rendering with vector blur throws glitches

Hi everyone

We are trying to render hair particles with Cycles, adding some vector blur, but we are getting random glitches like the ones found in the attached images. The eyebrows of this character are built with hair particles. The glitches don’t occur at every frame, but maybe in the 30% of all the frames. When we render the character from a distant camera it doesn’t happen, but as soon as we try to render it in a medium shot or close up, it throws this kind of glitches

This is the compositing node layout we are using

Any ideas?