My Vamo started experiencing this delayed firing issue after weeks of working fine. Someone else has reported that the replacement spring (gold color) will take care of this issue, and I have one on the way.
But, something I've found is that if I'm holding the Vamo and put my little finger on the end cap as I'm firing with my thumb, the delayed firing issue goes away. Take my little finger off the end cap, every few fires I'll get a delay. Weird, but it'll do until my spring arrives.