Dyno'd Today, Nitrous got cold feet

Hey everyone,

I finally went to get the car dyno'd today for the 1st time, with the intention of seeing what the spray has been doing for me.

1st pull, NA 300hp 285ftlbs.
2nd/3rd, nitrous is engaged and the car falls on its face and looses 50 hp with no nitrous even flowing. I even had to let off early.

I have been running a 125 dry shot for about 2 years with no issues, now this?? Its a basic zex kit, and I've never had the slightest hickup. The AFR looked good throughout, so what could cause this?