Do not be discouraged by a little setback. There is not a perfect zapper and no zapper can get rid of latent viral RNA hiding inside of a cell. The important thing to do during an outbreak is to zap more. The more viri that are killed, the less that opportunity for more repeats.
I feel very fortunate that I have not had any outbreaks of my oral herpes since a short time after I started zapping. It has been a little over 14 years since I first zapped.