Not sure if this is helpful, but ...
I had gotten some replacement 0-rings for the bolt guide at 'the o-ring store' on-line. I put them on, but it turns out they were too fat, and the bolt didn't slide along the guide very easily. My marker wouldn't fire correctly for the first several shots, then evened out. Maybe the o-rings and lube got warmed up from the friction. I got some more 0-rings from another source, and they seem to be working fine now.
Could something similar be happening to you? Does your bolt slide easily along the guide? Did you replace the 0-rings recently?
Here's a thread with a similar problem, and it was solved by cleaning the solenoid;